To add, they are adventure games, where you point and click where you want the character to go. Except for the 4th one where you control Guybrush (the main character) around with your arrow keys. But the idea is still the same with that one too, theres a story, and you go around solving puzzles to move forward in the story. Oh, and to fight pirates with more your witt than your sword. Insulting swordfighting, anyone?
And what a story they have made. It's one of the most brilliant games that has ever come out. No, I take it back, they ARE the most brilliant stories to have come out.
Other adventure games worth getting from LucasArts are Day of the Tentacle and Full Throttle. You'll have hours and hours of laughs from them.