If your neighborhood seems to teem with cats, that means there are a lot of cats running around. When something teems, it swarms or overflows with a large number of things.
Don't confuse teem with team. The two words may sound the same, but they have different meanings. Use the noun team when describing a group of people with a common goal, and turn to the verb teem for those times when you need to say that something is overflowing or crowded. Teem is almost always used with the preposition with, as when the busy streets teem with activity.