A boolean, or bool value, is a very simple type of data. It can be either true or false. (See BoolValue) That's it. In Lua, everything that has a value is treated as true when converted to a boolean, unless it is nil, false, or 0. Good for making a high advanced games.
A boolean is a bit, a bit can be either 1 or 0, and is the most important "component" in a computer. In this case 0 = false and 1 = true.
"The best thing about a boolean is even if you are wrong, you are only off by a bit"