It's the Apple Command ⌘ key, you might know it as:
Apple key, clover key, open-Apple key, splat key, pretzel key, propeller key, squiggly button, AppleSquiggle, hairball, funny key, butterfly key, the quad button, or meta key
It doesn't matter what you call it, most Mac users can't help but wonder, what's with this funny symbol?
Command Key History
The command key got its start as an Apple logo beginning with the Apple III. If you bought an Apple computer in 1980, you might remember this.
In 1984, with the introduction of the Macintosh and its graphical user interface, the Apple Key created a problem. The menus across the top displayed several commands you could select (like File -> Save), but it also displayed the keyboard shortcut you could quickly type instead of using the mouse.
The problem was that the menus were now littered with the Apple symbol. Steve Jobs is regularly quoted as saying that having the Apple logo repeated so many times in the menus was ridiculous.
"There are too many Apples on the screen! It's ridiculous! We're taking the Apple logo in vain! We've got to stop doing that!" -Steve Jobs
What he was really saying was that they were just over-using their own logo. As much as I enjoy Apple products, that much probably would have made them look like narcissists or worse, possibly dilute the brand. Smart thinking Steve!
Finding the Clover Symbol
Since Steve wasn't happy with covering his new menu system with his company's logo, the search began for a new symbol.
Susan Kare found the ⌘ symbol; at the time it was used in Denmark, Finland, Iceland, Norway, and Sweden to denote a tourist attraction. The shape represents a square castle with four round towers at each corner (when looking from above). She ran it by the team, it was well received and officially became the new symbol for the Apple key in 1984.
Phasing out the Apple Symbol
Although a new symbol was found, they couldn't completely remove the Apple symbol from all of their keyboards. The keyboards were meant to be backwards compatible and users of the older systems would be searching for the Apple key. The symbol was officially removed from all keyboards in 2007. But since it was on the keyboards for 27 years, talk to any long-time Mac user and they'll probably still refer to the Command key as the Apple key.