Need help understanding command I am having a problem with imported photos showing in thumbnail, but coming up blank with exclamation mark.  I am trying to follow suggestions found on the net.  But, I don't know what the symbol behind the command symbol means??  I assume it is another key, but don't see a corresponding one on my macbook.  HELP!!

Try repairing the library. Hold ⌘⌥ and open iPhoto, then choose Repair Database.

If that doesn't fix it, hold ⌘⌥ and open iPhoto again, and select Rebuild Database.
It's the option key. Also called the Alt key on a windows keyboard.

It's the key to the between command and control.