Boolean expressions
Boolean expressions are mathematical expressions that are either true or false. They're great for filters. Here are some Boolean expressions:
age = 30 (this is either true or false for each person in your data set)
price + tax < 10.00
3 > 4 (this is almost always false)
In contrast, regular mathematical expressions turn out to be numbers instead of true or false, so
3 + 4 is not a Boolean expression. Neither is
age + 12