The Lesson
A natural number is a whole number from 1 upwards:

Mathematicians use the symbol

to represent the set of natural numbers.
The Oxford English Dictionary defines a natural number as "a positive whole number (1, 2, 3, etc.)"
Natural Numbers As Counting Numbers
A natural number is a counting number.
Natural numbers are the numbers you would use to count objects.
Natural Numbers on the Number Line
The image below shows the natural numbers on the
number line.
Note: The natural numbers are whole numbers only. They are not found in between the numbers shown.
What Natural Numbers Are
Natural numbers are
positive integers.
What Natural Numbers Are Not
Natural numbers are
not negative (such as −1) and are
not fractions (part of a whole number, such as ½ or 0.3).
What Natural Numbers Are (Usually) Not
0 is (usually) not a natural number.
A child learning to count would not count zero objects.

(Some mathematicians do count 0 as a natural number. We do not. The idea of 0 is more abstract and less natural - it was invented later. If you include 0, you have the
whole numbers).