Description: Mysterious negative numbers! What ARE they? They are numbers less than zero. If you understand the nature of below zero temperatures, you can understand negative numbers. We'll help. Created by Sal Khan. In this video, I want to familiarize ourselves with negative numbers, and also learn a bit of how do we add and subtract them. What does a negative number even mean? But when we think about it, you probably have encountered negative numbers in your everyday life.*Teacher Advisor is 100% free.