Protein Powder: What Is It?

Ask anyone at your local gym what supplements he's taking and you will probably receive one of the following answers: 

"Whey" 
"Casein"
"Protein powder"
"Nothing. Too broke for that crap" 

Assuming you fall into one of the first three categories, you have probably been told that protein powder plays an important role in muscle recovery and speeds up the process of accruing mass so that you'll look like this guy in three months:

Two-Time Mr. Olympia, Phil Heath