A verb combined with an adverb or a preposition, or sometimes both, to give a new meaning.
fence something in
to enclose an area within a fence.
When they fenced the garden in, they thought the deer wouldn't be able to destroy the flowers.
Phrasal verbs are two or more words that together act as a completely new verb with a meaning separate from those of the original words.
A compilation of 50 phrasal verbs.