Newbie Mac tip: This symbol: refers to the option key, aka "alt." This symbol appears alongside menu items to indicate that the option key must be held down as part of the item's keyboard shortcut.

All the Mac users in the audience are laughing at me right now, but I'd like to point out that this symbol hasn't appeared on a Mac keyboard in years. The option key simply says "alt / option" on it. The command key has its symbol () on it, and the symbol for the shift key () is at least a little bit intuitive. The symbol for control (^) is traditional, but not terribly intuitive. A Mac Help search for "symbols for special keys" will produce a nice list.

I would have been able to figure it out in one or two guesses if it weren't for the fact that my first encounter with the option symbol was this menu item:

This means option + spacebar. That's totally not my fault.