It's like shared memory, but for texture memory in the GPU between separate heavy weight processes. Since simply sharing main memory between processes wouldn't be nearly as efficient, requiring frequent uploading and downloading textures to and from the GPU.
Mac OS/X and iOS IOSurface:
https://developer.apple.com/documentation/iosurface?language...
http://neugierig.org/software/chromium/notes/2010/08/mac-acc...
https://github.com/SimHacker/UnityJS/blob/master/notes/IOSur...
Android SurfaceTexture and GL_TEXTURE_EXTERNAL_OES:
https://developer.android.com/reference/android/graphics/Sur...
https://www.khronos.org/registry/OpenGL/extensions/OES/OES_E...
https://docs.google.com/document/d/1J0fkaGS9Gseczw3wJNXvo_r-...
https://github.com/SimHacker/UnityJS/blob/master/notes/ZeroC...
https://github.com/SimHacker/UnityJS/blob/master/notes/Surfa...