Game Center

Game Center is like a social network on your iPod touch, iPhone, or iPad.

Usage of N
In the descriptions, n is used to describe any number.

Friends
Through Game Center, you can add other gamers as your friends. You can play multiplayer games with or against your friends. In the leaderboard section for a game, it states that you are #n out of n friends.

Leaderboard
In the Leaderboard, there are two sections. One is for Friends and the other is for All n Players. There are three sections for the leaderboards, Today, This Week, and All Time.

Achievements
In some games there are achievements. You have to complete a task to get the achievement. Every achievement is worth a certain amount of points.