means Caught in a place or situation you cannot get out of, whether by physical confinement or by circumstances that close off every exit.

from From "trap," an Old English word (treppe, related to words for a step or to tread) for a snare laid to catch animals — the same image of a hidden mechanism that springs shut. The figurative sense of being "trapped" in a predicament, with no escape, follows naturally from the literal device that holds prey fast.