A belt bumper is an airport-security inconvenience: the person who leaves their tray or bag sitting on the conveyor and blocks everyone behind them. The result is a small, annoying pileup at the belt when people are just trying to grab their things and move on.
Человек, который после досмотра не убирает с ленты свой лоток или сумку и мешает остальным забрать вещи. Из-за него у ленты быстро возникает небольшая, но раздражающая пробка.
«We were all ready to leave, but one belt bumper had left a tray right in the way.»seen in Cambridge Dictionary