Apple key? do you mean Command?

When reading documentation I often found the terminologies referring to the Apple, Command, Option and alt keys very confusing, sometimes they are exclusively represented by symbols instead of their names, so I thought it would be useful to give you a quick overview with the help of Wikipedia.

Command key

The Command key, known as the open-Apple key in documentation previous to the Apple Macintosh family of computers, is a modifier key present on Apple keyboards. An “extended” Macintosh keyboard—the most common type—has two command keys, one on each side of the space bar. Compact keyboards have one only on the left.

Manuals and other documentation commonly uses the symbol ⌘ (U+2318 in decimal) to represent the Command key. The clover symbol has no official name, but is often given nicknames like ‘”splat”, “butterfly”, “squiggle”, “beanie”, “flower”, “cauliflower”, “propeller” or “shamrock.” Some believe the symbol to be named the “infinite loop”, which is also the address for Apple world headquarters: 1 Infinite Loop, Cupertino, CA 95014. Unicode standards documents call it the Place of Interest Sign.

Option key

The Option key, also known as Alt key is a modifier key present on Apple keyboards. It is located between the Control key and Command key on a standard Macintosh keyboard. For desktop keyboards, there are usually two, while a laptop may have only one to make room for the arrow keys.

The key usually has the word “alt” written above “option” as well, for compatibility with Windows programs running under emulators, as well as Unix programs. In Mac OS X and Mac OS 9 however, it functions differently from the Alt key under Microsoft Windows and Unix-like systems. Most notably, it is not used to access menus or hotkeys, but is instead used as a modifier for other command codes, and also to provide easier access to various accents and symbols.

Apple commonly uses the symbol ⌥ (U+2325, 8997 in decimal) to represent the option key. This symbol represents a microswitch, allowing the current to go one of two directions.

You can read more about the Option and Command keys on Wikipedia.