Butterfly Back Earrings
https://www.storeboard.com/blogs/fashion/butterfly-back-earrings/5533270

Butterfly Back Earrings
The most popular style of earring backing is the Butterfly Back Earrings, which also goes by friction back and push-back closure. This earring fastener relies on tension to secure itself around the earring post. As a result, you'd reposition the earring back on the piercing post until it gently but firmly abuts the earlobe and then secures it.
https://www.storeboard.com/blogs/fashion/butterfly-back-earrings/5533270

A Brief Overview Of Butterfly Back Earrings
The most popular style of earring backing is the Butterfly Back Earrings, which also goes by friction back and push-back closure. This earring fastener relies on tension to secure itself around the earring post. As a result, you'd reposition the earring back on the piercing post until it gently but firmly abuts the earlobe and then secures it.
https://www.storeboard.com/blogs/fashion/butterfly-back-earrings/5533270