勒 (lēi) means to compel or force someone to do something, in a colloquial, often physical or pressing way (e.g., "别勒我" = don't force me). It is less formal and more direct than 强迫 (qiǎngpò, formal compulsion), and implies a kind of straining or tightening pressure, unlike 逼 (bī) which is more about cornering or pressuring.