A number is an idea that is used to count or measure something. It is really just in our minds. We use numerals to represent numbers.

In the picture, Lucy is thinking of a number: the number "one", because she is thinking of one ball. If she wanted to communicate that idea to us, she'd probably bark once, or thump her tail on the floor once.

There are many different types of numbers. Some of them are whole numbers (1,2,3,4, etc), integers (-1,0,1, etc), decimals (-1.73, 2.578 etc) and fractions \(\left(\dfrac{1}{2}, \dfrac{23}{38}\right)\).