What is a league in starcraft

In Starcraft II: Wings of Liberty a league is a classification, or distinction system, of different playing abilities of players.
Leagues of Starcraft II:

• Bronze
• Silver
• Gold
• Platinum
• Diamond
• Masters
• Grandmasters

Each player is placed within a league after playing his/her placement matches. A player can advance or fall within a lower league depending on game performance.