You can declare a BOOLEAN PL/SQL variable type. There is no BOOLEAN database column type.
Booleans are easy to work with. Often the existence of a value logically relates to a Boolean variable. For the student's demo, a student can have several majors (e.g., Biology). One valid lookup value is: Undeclared. Suppose you consider Undeclared to be FALSE and any other major to be TRUE. Logically this equates to: having a major is TRUE. Having an undeclared major is false. Such a scenario can be common in application code.
It helps to have a package that maps Boolean values to a 1 and 0. For example, the following package is a general purpose package that transforms a Boolean to and from a zero or one.
CREATE OR REPLACE ...