Every 25 years there is a Quarter Quell edition of the annually Hunger Games.
Quells mark the anniversaries of the districts' defeat by the Capitol, and include special celebrations.
So, the the 75th Hunger Game will as known as The 3rd Quarter Quell Hunger Game too.

[img=http://www.myhungergames.com/wp-content/uploads/2012/01/Catching-Fire-Arena.jpg]
The arena of the 3rd quarter quell hunger game.
As you can see, the quarter quell has more traps, dangerous things than normal annually hunger game,
just to make the tributes harder to survive or win.