The "truth value" of a statement is the true or false -ness of that statement. If you can evaluate something to be true or false it has a truth value.

6 > 5 ... has a truth value of: true
6 > 7 ... has a truth value of: false
5 ... has no truth value because it cannot be evaluated any further.

You can also obtain truth values for other kinds of statements such as "The sky is blue".