# Definitions

## number

48px number
A number is a concept from mathematics, used to count or measure. People use symbols to represent numbers; they call them numerals. Common places where numerals are used are for labeling, as in telephone numbers.

In arithmetic, addition is finding the total of two or more numbers. The sign for addition is "+". The name for the sign "+" is "plus".

## subtraction

48px subtraction
Subtraction is the arithmetic operation for finding the difference between two numbers. The expression 7 − 4 = 3 can be spoken as "seven minus four equals three," "seven take away four leaves three." The sign for subtraction is "−". The name for the sign "−" is "minus".

## keyboard

48px keyboard
A computer keyboard is an important device that allows a person to enter symbols like letters and numbers into a computer. It is the main input device for most computers.

 A common symbol for the enter key It is usually found near the middle of the right hand side of the keyboard.