Stud, lever back or clip-on earrings ?
Stud earrings are constructed on the end of a post, which penetrates straight through the ear or earlobe. A "butterfly" slides on the post behind your ear lobe.
Lever Back - The back is curved like a fish hook with an enclosure that latches behind the ear.
The clip-on is a two-part piece attached to the back of an earring. The two pieces closed around the earlobe, using mechanical pressure to hold the earring in place.