Uninstalling applications in Mac OS X is very different than uninstalling in a Microsoft Windows environment because Mac OS X has nothing like the Windows Registry. 

While most Windows programs include an uninstaller that can be run through using the Add/Remove Programs control panel, no such feature exists in Mac OS X and so most users simply move application bundles (see below) to the Trash. However, often times there is more to uninstalling than a simple drag-and-drop to the trash.

Most Mac OS X applications (anything that ends in .app), like Safari and iTunes, are bundles. The application icon you see in Finder (typically the Applications Folder) is usually a special folder itself, made to appear as a single double-clickable file. These “folders” contain all, or at least most, of the files needed to run the application, ie they are self-contained. This means that to uninstall these applications, you only have to drag them to the Trash. If you control-click (or right-click) on an Application icon, and you see “Show Package Contents”, then it is a bundle.Isn’t it cool ? just deleting one file from /applications/ folder.

- courtesy: macrumors.com