When you delete a file or folder on a Macintosh computer, it is stored in the Trash. In early versions of the Mac OS, the Trash was located on the desktop, but in Mac OS X, it is found in the Dock. The Trash icon is an empty trash bin when the Trash is empty and changes to a full trash bin when there are items in the Trash.
The Trash serves the same purpose as the Windows Recycle Bin. Items can be moved to the Trash by selecting them and dragging them to the Trash icon. You can also choose "Move to Trash" from the Finder's File menu or press Command-Delete after selecting one or more items. You may view items in the Trash by clicking the Trash icon in the Dock. Since the items stored in the Trash have not been permanently deleted, you can drag items out of the Trash if you wish to keep them.
Emptying the Trash
If you are sure you want to permanently delete the items in the Trash, you can press the "Empty" button in the Trash window or right-click anywhere within the window and select "Empty Trash." You can also empty the trash without even opening the Trash window by selecting "Empty Trash..." from the Finder menu. If you want to overwrite the deleted data so it cannot be recovered even with a data recovery utility, you can select "Secure Empty Trash..."
NOTE: If you wish to delete locked items that are stored in the Trash, hold the Option key while selecting "Empty Trash."