A Login can come in the form of a username and password, perhaps further authenticated by a second or multiple methods (multi-factor authentication). It could also just be solely a thumbprint, facial recognition scan or access card. This login information is used to attempt to assure that the person entering the information is the legitimate user. The login provides access to, and potentially rights to do things with, data or systems that hold or transmit data.
Adapted from Ernst (2013)