What is the "good and bad fruit?"?

In Matthew 7:15 it says,"Watch out for false prophets. They come to you in sheep’s clothing, but inwardly they are ferocious wolves. By their fruit you will recognize them. Do people pick gs from thorn bushes, or figs from thistles? Likewise, every good tree bears good fruit, but a bad tree bears bad fruit." What exactly is the fruit that it is talking about? Is it how they act or what they teach or something like that?