EGL™ is an interface between Khronos rendering APIs
such as OpenGL ES or OpenVG and the underlying native
platform window system. It handles graphics context
management, surface/buffer binding, and rendering
synchronization and enables high-performance, accelerated,
mixed-mode 2D and 3D rendering using other Khronos APIs.
The reference pages describe the latest approved version of EGL, EGL 1.4, but can be used with earlier versions since each page notes when features are available only starting with specific versions (1.2, 1.3, and 1.4).
A more detailed overview of EGL functionality and technical concepts can be found in the eglIntro page.