背黑锅 is a common idiomatic expression meaning 'to take the blame for someone else' or 'to be made a scapegoat'. The literal image is 'carrying a black wok' on your back — the black wok symbolizes undeserved shame or guilt. It functions as a separable verb (离合词): the object 黑锅 can be separated from 背 by aspect markers, measure words, or other modifiers (e.g., 背了黑锅, 背过一次黑锅). You often use it with a beneficiary introduced by 替 or 为 ('for someone else').