Draw Something Guess Cheat is when the player writes out the words instead of drawing it. This happens most often when you're playing a random matchup with a stranger. Draw Something was designed to be played with friends, but sometimes your friends might not be playing the game, so you'd have to pair up with a stranger.
Draw Something Guess Cheat is a problem because it takes the fun out of the game, people do it to earn coins quickly, so that they may buy paint or bombs but it makes the game incredibly boring.
When you run into a cheater, the best thing you can do it to exit the game, these people are ruining the game. When you exit the game, Draw Something keeps track of how many people have cancelled their matches with the cheater, and it'll get more difficult for the cheater to find matches in future.
Here's an example of a cheater