Call of Duty: Modern Warfare 2 - Stimulus Package

Summary pulled directly from Steam - Some text may only be applicable to Steam platform

The Modern Warfare 2 Stimulus Package delivers additional action-packed multiplayer maps, including brand-new battlegrounds and legendary fan-favorites from Call of Duty 4: Modern Warfare.
When purchased, this content will be automatically downloaded and incorporated into the game; DLC will not be listed as a separate entry in your Steam Library.
To view the additional content, please do the following:
1) Log in to Steam
2) Navigate to your Library list
3) Right-click on the game
4) Select "View downloadable content".