Forcing Function
A design feature that makes a specific error physically impossible until a required step is completed.
In practice
A forcing function blocks a mistake by making it impossible to continue until a required step is done. A car that will not shift out of park unless the brake is pressed, a microwave that stops when its door opens, and a form whose submit button stays disabled until required fields are filled are all examples. Designers use forcing functions where errors are costly, accepting a small inconvenience to prevent them.
Often confused with Affordance
An affordance suggests how something should be used; a forcing function prevents the wrong action outright until the correct step happens.
Try this
List three devices at home that refuse to work until you do something first, and note which error each prevents.