An act of falling back.

A backup plan or contingency strategy; an alternative which can be used if something goes wrong with the main plan; a recourse.

“As a fallback, I suppose we can use typewriters if the word processing system fails.”

A reduction in bitumen softening point, sometimes called refluxing or overheating in a relatively closed container.

That can be resorted to as a fallback.

“a fallback plan”