Jekyll is a simple, blog-aware static site generator written in Ruby. It allows users to create websites by writing content in plain text files, which are then transformed into a complete website. Jekyll is often used with GitHub Pages, making it easy for developers to host their projects online without needing a database or server-side processing. Jekyll uses a templating system to manage layouts and includes features like markdown support, which simplifies formatting text. It is popular among developers and bloggers for its ease of use and flexibility, enabling them to focus on content creation rather than technical details.