Booleans
Less than 1 minute
Introduction
A boolean is a value that can be either True or False. They are quite useful and are used all the time in programming. A variable can be a boolean.
You should try to name your booleans (variables and functions) positively. It makes it harder to misunderstand their meaning and get them wrong.
Wrong names: playerDead, invoicePaid, userNotExists()
Correct names: playerAlive, invoicePaid, userExists()