Party
A party, in the context of role-playing games, is a group of player characters working together. Generally, given a group of players, one will be the GM/DM/ST/Aedile, and the other players will take control of the player characters in a party. A party does not need to contain solely Player Characters, and various NPCs may or may not join the party, at the GM's discretion, when the plot demands it, or when players get goofy.
Never split the party. I'm serious, man, it's a bad idea.