Open the Last Closed Tab in Safari on the Mac
Safari lets you undo your action of closing a tab--as long as you act promptly. If you close a tab by mistake and then open a new tab, you won't be able to restore the closed tab with the shortcut below, because the undo feature only works on your last action.
In OS X, after closing a tab, press Command+Z, the standard Mac keyboard shortcut for Undo. Your lost tab will be instantly restored. Alternatively, you can go to the Edit menu and select "Undo Close Tab".