When doing fat grafting, BBL, what does 1600cc mean? Is this pure fat?

A cc is equivalent to a mL. One way to look at that is to think of a bottle of water. The standard bottle of water is 500mL, so 500cc would be the same volume as a bottle of water. 1600cc is roughly 3 bottles of water. It is actually not pure fat although we do all sorts of techniques to try to get it as pure as possible. One of the reasons why the buttocks shrinks is secondary to absorption of any fluid that was mixed in with the fat. This shrinkage happens early. The volume loss that happens a little slower over the first 3-6 months is actual fat death. 

A cc means cubic centimeter. It is a measure of volume. It is used for volume of implants, fat injections, fillers and any time to measure volume