Phrasal verbs, also called two-word verbs, are idiomatic expressions wherein the second element of the verb (the adverb or particle) is not necessarily predictable.
Phrasal Verb:
break down
Meaning / Example:
1. [for something] to fall apart; [for something] to stop operating. > The air-conditioning broke down, and we got very warm. > The car broke down on the long trip.
2. [for one] to lose control of one's emotions; [for one] to have an emotional or psychological crisis. > He couldn't keep going. He finally broke down.