The Steam application is required to play all games purchased through Steam, as well as retail games registered to Steam.
Just dragging the Steam program to the Trash will not fully uninstall Steam. The additional steps below are required.
The following instructions will describe how to remove Steam and, optionally, all your games from this computer. If you complete all the steps and decide to reinstall Steam later, you will need your account name and password to reinstall your games.
With the Steam application active, click the Steam menu and Quit Steam to exit Steam.
If you don't want to lose any game data: delete all files and folders in /Steam EXCEPT FOR the /SteamApps folder (this contains your game downloads and any local save files.)
If you're removing all Steam data from your computer: delete the entire Steam folder.
With these files deleted, you can reinstall Steam if you are troubleshooting a problem.