This is the name of the lens mount used by Sony mirrorless cameras. Regular E-mount lenses fit its APS-C format cameras, like the Sony A6500, while FE lenses fit its full-frame mirrorless cameras, including the A7 series and Sony A9. Sony also makes A-mount lenses for its Alpha SLT cameras, but these are not the same.
This is the physical connection between a lens and the body of a DSLR or mirrorless camera. It consists of a twist-lock bayonet mount and electrical connectors. The lens mount is specific to a camera brand – you have to make sure you get lenses in the right fitting for your camera.