1  Natural numbers

A natural number is a number that can be used in counting, i.e. 1, 2, 3,… Sometimes zero is also included as a natural number. Natural numbers have two main purposes, counting (e.g. ‘my car has 4 wheels’) and ordering (e.g. ‘I came 4th in the race’).

2  Directed numbers

A directed number has either a + or a – sign in front of it. The + sign indicates that the number is higher than zero, and the – sign indicates that the number is lower than zero. Numbers less than zero are called negative numbers.

3  Integers

The integers are defined as the natural numbers (1, 2, 3,…), their negatives (-1, -2, -3,…), and the number zero.