Well to start off, FreePlay is basically defined as credit to play in a slot machine for free in order to win real money. Anything you make off of the FreePlay, is yours to keep...or play with.
Free spins are a type of promotional offer that you can get when playing at an online casino. Simply put, you get a certain number of attempts in advance that can be used on a particular slot machine. They come in the form of no-deposit bonuses or as part of deposit bonus packages.