fall-back

noun

1. An act of falling back.
2. 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.”
3. A reduction in bitumen softening point, sometimes called refluxing or overheating in a relatively closed container.
4. Pulverised material that falls back to earth after a nuclear explosion; fallout.