Booleans represent logical values that can only be TRUE or FALSE. They are fundamental to conditional logic in Google Sheets formulas.
Other data types can behave like Booleans in certain contexts. Such values are known as “truthy” and “falsy”. While not genuine Booleans, these values can be coerced to logical equivalents.
For a complete reference of how Sheets coerces types, see Type Coercion.
In Google Sheets, checkboxes correspond directly to Boolean values by default—checked for TRUE, and unchecked for FALSE.