OpenGL is a
graphics API that was initially created by Silicon Graphics in 1992 for their 3D workstations. OpenGL is a specification this means the manufacture of your graphics driver has taken the liberty to write the code for OpenGL.
OpenGL is a state machine API, this is expressed through functions such as glBindBuffers(), glUseProgram().
OpenGL has been used in
popular game engines such as Unity.
However, nowadays OpenGL has been
deprecated on many systems in favor for Vulkan, a more verbose graphics API.
tldr; OpenGL shows cool ass graphics