If a ceiling, roof, or other structure caves in, it breaks and falls into the space below.

Because of the explosion, the roof of the building caved in, trapping several people. 由于发生爆炸，建筑物的顶部坍塌，有几个人被困在了里面。

to cave

At first, they refused to sign the agreement, but they caved in when they heard another firm was being approached. 起先，他们不肯在协议上签字，但听说我们正跟另一个公司接洽就答应了。