A whole number is any number you can count without using fractions or parts. The whole numbers are 0, 1, 2, 3, 4, 5, and so on, continuing forever. They're called “whole” because they represent complete, undivided amounts.

When you count students in your class, books on a shelf, or days until your birthday, you're using whole numbers. You can have 23 students or 24 students, but not 23.5 students. You can save $15 or $16, but you don't have a whole number of dollars if you have $15.50.

Whole numbers don't include negative numbers like -3 or -10. They also don't include decimals like 7.2 or fractions like ½. If you can represent it with your fingers or with blocks without breaking anything into pieces, it's probably a whole number.

Some people use the term “whole number” to mean 0, 1, 2, 3, and so on. Others use it to mean 1, 2, 3, and so on, without zero. In this dictionary, zero is counted as a whole number.

The concept matters when you're measuring things that can't be divided. You might run 5.7 miles, but you can't read 5.7 books (you either finished the sixth book or you didn't). Understanding whole numbers helps you recognize when partial amounts make sense and when they don't.