Definitions

Here are basic definitions that are needed to undestand the concepts.
A Boolean value is either True or False. A Boolean variable may only take on a Boolean value. The negation of a Boolean value is the other Boolean value (e.g. the negation of True is False).

A Boolean expression is defined recursively as follows:
Each of the following is a Boolean expression: a Boolean value, a Boolean variable, the negation of a Boolean expression, the conjunction of two Boolean expressions, the disjunction of two Boolean expressions.