Phrasal verbs are idiomatic expressions in English that are formed by combining a verb with a preposition or adverb. This creates a new meaning that is different than the single verb alone. Some common phrasal verbs include "break down" which means to stop working, "turn on" which means to light or power something on, and "come back" which means to return. Phrasal verbs are very commonly used in both written and spoken English. They add complexity but also nuance to the language.