Headless software – Wikipedia
Headless software (e. g. “headless Java” or “headless Linux”, ) is software capable of working on a device without a graphical user interface. Such software receives inputs and provides output through other interfaces like network or serial port and is common on servers and embedded devices.
The term “headless” is most often used when the ordinary version of the program requires that a graphics card or similar graphical interface device be present. For instance, the absence of a graphic card, mouse or keyboard may cause an initialization process that assumes their presence to fail, or the graphics card may be relied upon to build some offline image that is later served through network.
A headless computer (for example, and most commonly, a server) may be missing many of the system libraries that support the display of graphical interfaces. Software that expects these libraries may fail to start or even to compile if such libraries are not present. Software built on a headless machine must be built within command line tools only, without the aid of an IDE. 
Next to headless computers and headless software, the newest form of headless technology can be found in websites. Traditional websites have their own back-end and front-end (graphical user interface). All the pieces work with the same code base and communicate directly with each other, making the website as a whole. However in a headless installation the front-end is a stand-alone piece of software, which through API communicates with a back-end. Both parts operate separately from each other, and can even be placed on separate servers, creating a minimum version of a multi-server architecture. The bridge between both parts is the API client. The endpoints of the API are connected to each other.
The biggest advantages of this technology can be found in performance optimisation and flexibility of the software stack.
^ Clarification of “headless mode” for Java case
^ Clarification of “headless Linux”
^ “A discussion relevant to the headless builds”. Archived from the original on 2013-06-23. Retrieved 2013-05-17.
^ Michael Wiles (2010) Headless Build, who needs it?
Definition of headless – Merriam-Webster
Recent Examples on the Web
Consider, for instance, Venus Restored (1936), in which the headless white bust of classical antiquity is bound in ropes.
Jeremy Lybarger, The New Republic, 7 Oct. 2021
The drone comes with a headless mode function and a one-key take-off/landing, in addition to the aforementioned altitude hold function.
Chris Hachey, BGR, 4 Oct. 2021
Numerous companies are seeing fantastic results from headless eCommerce.
Ben Sekhon, Forbes, 4 Oct. 2021
They were highlighted by Insider as being part of headless companies.
Walter Loeb, Forbes, 3 Sep. 2021
At Disney California, grown-ups can pose in front of a full-size headless horseman sculpture in Carthay Circle, and children can enjoy posing in front of the less-scary Cars Land car sculptures dressed in Halloween costumes.
San Diego Union-Tribune, 7 Sep. 2021
Mayank Mishra is the VP of Engineering at Contentstack, the pioneer in API-first, headless CMS technology.
Mayank Mishra, Forbes, 10 June 2021
Only Slattery — who’s been captive in Wenwu’s China compound for years as a kind of court jester — knows how to find Ta Lo, via his uncanny ability to communicate with an adorable, headless creature from that world.
Adam B. Vary, Variety, 3 Sep. 2021
So, for a little extra creepy factor, feel free to carry around a headless doll to complete Wednesday’s look.
Chaise Sanders, Country Living, 2 Sep. 2021
These example sentences are selected automatically from various online news sources to reflect current usage of the word ‘headless. ‘ Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.
Headless content management system – Wikipedia
A headless content management system, or headless CMS, is a back-end-only content management system that acts primarily as a content repository. A headless CMS makes content accessible via an API for display on any device, without a built-in front-end or presentation layer. The term “headless” comes from the concept of chopping the “head” (the front end) off the “body” (the back end). 
Whereas a traditional CMS typically combines the content and presentation layers of a website, a headless CMS comprises just the content component and focuses entirely on the administrative interface for content creators, the facilitation of content workflows and collaboration, and the organization of content into taxonomies.  As such, a headless CMS must be combined with a separate presentation layer to handle design, site structure and templates.  That combination generally relies on stateless or loosely coupled APIs. 
One advantage of this decoupled approach is that content can be sent via APIs to multiple display types,  like mobile and Internet of Things (IoT) devices, alongside a website.  A disadvantage, however, is the requirement to maintain two separate systems for a single site, which can require more resources. 
Cloud-first headless CMSes are those that were also built with a multitenant cloud model at their core and whose vendors promote software as a service (Saas), promising high availability, scalability and full management of security, upgrades and hotfixes on behalf of clients.  Similar to how headless CMSes focus on creating content in the backend to be displayed on frontends via APIs, headless commerce uses the same setup to separate backend product management and navigation from the frontend of a website or other display types, like IoT. 
Headless CMS is similar to but distinct from the use of widgets or plugins on a site, like adding an Uber Eats menu or online ordering plugin to a restaurant website. 
Most headless CMS platforms employ a version of these features:
Roles and permissions
Content types and taxonomy
Coupled CMS vs. headless CMS
Most traditional or monolithic content management systems are “coupled, ” meaning that the content management application (CMA) and the content delivery application (CDA) come together in a single application, making back-end user tools, content editing and taxonomy, website design, and templates inseparable.  Coupled systems are useful for blogs and basic websites as everything can be managed in one place. However, in a coupled CMS, CMS code is tightly connected to any custom code and templates, which means developers have to spend more time on installations, customizations, upgrades, hotfixes, etc. and they cannot easily move their code to another CMS.
There is a lot of confusion around the differences between a decoupled CMS and a headless one because they have a lot in common; a headless CMS is a type of decoupled architecture.  Like a headless CMS, a decoupled CMS separates the CMA and CDA environments, typically with content being created behind the firewall and then being synchronized and pushed to the delivery environment. The main difference between a decoupled CMS and a headless CMS is that the decoupled architecture is active—it prepares content for presentation and then pushes into the delivery environment—whereas a headless CMS is reactive—it sits idly until a request is sent for content.
Decoupled architecture allows for easier scalability and provides better security than coupled architecture, but it does not provide the same support for omnichannel delivery. Plus, there are multiple environments to manage, hiking up infrastructure and maintenance costs. 
Another simpler way to understand the difference between a decoupled CMS and headless CMS is on the basis of inclusion of front-end in the offering. decoupled CMS would always have a front-end included in the offering though connected with an API and hence following the decoupled architecture. On the other hand, a headless CMS does not offer front-end at all but an API using which content is served.
Criticisms and disadvantages
A headless CMS can also present challenges or drawbacks for teams and organizations, like:
A heavier technical proficiency requirement. 
Management of multiple systems, which can be challenging and a team’s knowledge base must cover all systems.
Fewer or no templates or out-of-the-box solutions.
Lack of channel-specific support. Since pure headless CMSes don’t deal with the presentation layer, developers may have to create some functionality on their own, such as website navigation.
Content organization. As pure headless CMSs do not typically provide the concept of pages and web sitemaps, content editors need to adapt to the fact that content is organized in its pure form, independently on the website or other channel.
Software as a service
Agile software development
^ a b Garcia, Veronica; Writer, Staff (2021-02-15). “Should your content management system go headless? “. The American Genius. Retrieved 2021-02-25.
^ Davis, Kim (2021-04-13). “The rise of headless and hybrid CMS: Tuesday’s daily brief”. MarTech Today. Retrieved 2021-04-19.
^ Edwards, Roy (2021-02-05). “Contentstack unveils its project Venus – enhanced headless CMS -“. Enterprise Times. Retrieved 2021-02-25.
^ “Headless CMS explained in 1 minute”. Contentful. Retrieved 25 January 2021.
^ “Headless CMS explained in 5 effective minutes”.. Retrieved 2021-09-02.
^ Lamoureux, Chris (2019-07-04). “What Is Headless CMS? Pros & Cons of Decoupling Your CMS – Veriday Blog”. Veriday. Retrieved 2021-04-19.
^ Petr Palas. “Why 2017 Is the Year of Cloud-First Headless CMS”. Retrieved 2017-01-30.
^ Stephen Griffin. “Cloud-First Headless CMS: What It Is and Why You Should Use It”. Retrieved 2017-02-07.
^ Levitz, Michael (2021-02-10). “3 Ways Covid Changed E-Commerce Forever: Your online store is now your flagship. Here’s how to make it pop”. Inc (magazine).
^ Mortazavi, Alireza (2020-09-14). “Headless CMS vs WordPress vs Custom Solution [Tech Debates]”. Medium. Retrieved 2021-02-25.
^ Mixon, Erica (2020-10-28). “Headless CMS powers personalized, omnichannel e-commerce”. TechTarget. Retrieved 2021-02-25.
^ Heusser, Matt. “An overview of headless architecture design”. SearchAppArchitecture. Retrieved 2021-04-19.
^ Deane Barker. “The State of the Headless CMS Market”. Retrieved 2017-02-08.
^ Brent Heslop. “A History of Content Management Systems and the Rise of the Headless CMS”. Retrieved 2019-01-12.
^ Kaya, Ismail. “Do You Need a Headless CMS? Maybe, Maybe Not”. Retrieved 2021-04-19.
Tamturk, Venus (December 16, 2016). “The Ultimate Guide for Headless Content Management Systems”. CMS-Connected. Retrieved 2018-06-07.
Frequently Asked Questions about headles
What does headless mean?
1a : having no head. b : having the head cut off : beheaded. 2 : having no chief. 3 : lacking good sense or prudence : foolish.
What’s a headless API?
A headless CMS makes content accessible via an API for display on any device, without a built-in front-end or presentation layer. The term “headless” comes from the concept of chopping the “head” (the front end) off the “body” (the back end).
What does headless mean in technology?
Headless software (e.g. “headless Java” or “headless Linux”,) is software capable of working on a device without a graphical user interface. … The term “headless” is most often used when the ordinary version of the program requires that a graphics card or similar graphical interface device be present.