isr.co.ro : glossary Boolean As applied to search operations, a mode that lets you specify multiple words or phrases combined with the words and, or, and not. For example, you might select pizza and toppings not anchovies. More generally, any system of logic that deals only in true and false values plus the combinations made up of those values and the operators and, or, and not. A programming variable that can only take on a true or false value.