Autofill relates to auto-populating data into user interface forms, etc.
Autofill is an option found in software programs such as Internet browsers that allows the users to quickly fill out common forms, with fields such as their address, e-mail, or credit card information.
For example, in a traditional shipping form you see when ordering something on-line: with Autofill you can select a field in the form, choose data you want to enter, and immediately have all fields filled out.