A number is an idea that is used to refer to amounts of things. People use number words, number gestures, and number symbols. Number words are said out loud. Number gestures are made with some part of the body, usually the hands. Number symbols are marked or written down. A number symbol is called a numeral. When we read a numeral out loud, we say the number word for that numeral. When we want to write a number, we can write the numeral or the word. For example, we say the word five and write the numeral 5 or the word five. The number is the idea we think of when we see the numeral or when we see or hear the word.

There are several kinds of numbers. Cardinal numbers tell how many things there are, as in "There are five people in my family." Ordinal numbers tell the position of something in an ordered set. For example, "I am sixth in the queue for lunch." Denominate numbers tell how many units of something there are, as in "I weigh 32 kilograms."