A number is a sign. It is used to describe a quantity of objects, animals or people, and it makes it easier to remember this quantity. Numbers can be used to calculate or to tell another person, for example, how much ice cream they get for their money.
The individual number signs from 0 to 9 are also called digits. You can also put together large numbers from several digits, for example, a million from a 1 and six zeros. In mathematics, this is also called the "decimal system".
Numbers have been around for a long time. In the past, they were simple strokes, sometimes objects were painted on them. The ancient Romans used certain letters as numbers, for example X for 10 or M for 1000. Only much later did they adopt the Arabic numerals that we use today.
Zero is a special number. It is not only the sign for "nothing", but also helps to write large numbers. It is not only the value of the sign itself that matters, but also where it is placed. A 100 is therefore more than a 10, and 1100 is more than 1001. Our numbers where the place matters are also called decimal numbers.
There are also other special numbers. For example, there are prime numbers. There are also numbers that have their own name, for example pi. It is often written with the Greek letter: π. These are usually numbers that have great significance in science: With pi, for example, you can calculate how large the area of a circle is.