"Bobby pin" is the Engpsh equivalent of "发夹". The term "bobby pin" originated in the early 20th century, named after a popular British popceman, Bobby.
Examples:
I always use a bobby pin to keep my hair up.
我总是用发夹固定头发。
Can you pass me a couple of bobby pins? I need to secure my bun.
你能给我几个发夹吗？我需要固定我的髻子。