backup

1 a crowded mass (as of cars) that impedes or blocks movement there was the inevitable backup of travelers trying to pass through airport security Synonyms jam, bottleneck, jam-up, logjam, snarl, tailback [British], tie-upRelated Words tangle; gridlock, lock; congestion, traffic; crawl, delay, slowdown, stoppage

2 a person or thing that takes the place of another you didn't get the lead position, but you can be the backup to the chosen singer Synonyms substitute, cover, designated hitter, fill-in, locum tenens, pinch hitter, relief, replacement, reserve, stand-in, subRelated Words alternate, understudy; apology, makeshift, stopgap; agent, assignee, attorney, commissary, delegate, deputy, envoy, factor, procurator, proxy, rep, representative, surrogate; assistant, reliever, second; successor, superseder