The digit 0 represents nothing.
Zero is used when there is no quantity present — no objects, no items, nothing to count.
This may seem simple, but “nothing” is an idea rather than a physical thing.
When counting real objects, we usually begin at one. If you have one apple, you count “one”.
If you have no apples, you would not normally begin counting at all.
In this sense, counting numbers traditionally begin at one, not zero.
For many centuries, zero was not used. If you had no goats, you did not go to market — there was nothing to count, and no number for it.
More about this can be found in the history section.
Although it represents nothing, zero is essential in modern mathematics.
Zero is unusual. It represents the absence of something, yet it behaves like a number.
In mathematics, zero is treated as a number in its own right. Different systems define “numbers” in different ways.
See general principles for more on this.