Abandonware - An illegal way to download games that are no longer sold in stores (but may or may not be sold on the Internet). Although many think it's legal, it's not. Not as illegal as warez, though.
Freeware - Full versions of games that are not sold and never will be sold. For example, Jetpack is freeware now.
Shareware - The old term for demo. Shareware is demo, and demo is shareware.
Demo - A shorter version of a game that just shows off the capabilities and main concept of the game. Often released several months before the game is released. I once found a demo version of Major Stryker in a store, but it didn't say it was a demo and not the full version. It was only like $2.00, so I got my mom to buy it for me. When I got home, I found out it was the same shareware version I all ready had gotten from a FREE demo disk. I was really angry, too. I don't know if what the store did, selling shareware, is legal, but if I remembered what store it was, I would SUE SUE SUE SUE SUE >OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO OO
Warez - A highly illegal way of getting free games that are still sold. Some games that are available through warez haven't even come out yet. Warez is often associated with ****ographic material, and hacking.
Full version - The full version of the game that you BUY. OMGOMGOMGOMG BUY!!!11 ;o
Trial - Versions of full games that can only be used for a limited time. You often get buggy trial programs that exceed the trial's limit. For example, I had the program Mozart for all most two years and it was supposed to stop working after two months. Trial versions of games and programs also are occasionally based on the number of times you use them. I've played some really nasty trial games that shut the game off when you lose, or win the whole game, or something, just so when you start it back up, you wasted one of your chances to use it. REALLY NASTY PEOPLE. Trial versions are often turned into full versions by codes, or serials. Hackers take advantage of this and often find out special codes that gives you the full versions, also known as crack codes.

PS: Is this thread ever going to die? =P