Abbreviation of authentication.
"The login screen asks you to enter your user ID and auth before granting access."
In plain English: Auth is short for authentication, which means proving who you are to get access to something online.
"Please verify that the auth on your package is signed before you leave for work."
To authenticate.
"The security expert used his digital auth to verify that the software update was genuine and safe to install."
A surname.
"The Auth family has lived in that valley for generations."