After is a preposition meaning "later in time" or "behind in space." After many hours of dancing, you'll be sweaty and hungry.
The word after goes all the way back to Sanskrit (meaning "further off" or "beyond"). You can use it in the context of time, as in, "Meet me after dinner and we'll take a walk," or of space, as in, "After you pass the school, you'll see the library on your right." After can also be an adverb. If you like ships, you'll recognize the relationship of after to aft, which means the rear part of the ship.
