sign in

Short definition from Wiktionary

Verb

1. 1
   To sign one's name on a list when entering a place, to indicate one's arrival.
2. 2
   To take some action to access a secured program or web page on a computer; to log in.
3. 3
   Misspelling of sign in.

Noun

1. 1
   The process or an instance of signing in.