Finger spelling (aka fingerspelling and finger-spelling)
is spelling out a word or name in
sign language, when there is no sign for the word, or
you don't know it.
Finger spelling is predominantly used when introducing
a new person to the conversation or when a sign isn't
known by one of the participants of a conversation.
The Deaf culture usually uses deaf names rather than
spelling out a persons name
each and every time.