A keypad is a set of buttons arranged in a block or "pad" which usually bear digits, symbols and usually a complete set of alphabetical letters. If it mostly contains numbers then it can also be called a numeric keypad. Keypads are found on many alphanumeric keyboards and on other devices such as calculators, push-button telephone

Push-button telephone

The push-button telephone was first invented in 1941, and is a telephone with push-buttons or keys, and which eventually replaced rotary dial telephones that were first used in 1891. The first push-button telephone was invented in the labs of Bell Telephone; however, these models were only...

s, combination locks, and digital door locks, which require mainly numeric input.

As a general rule, the keys on calculator-style keypads are arranged such that 123 is on the bottom row. Whereas, in a telephone keypad

Telephone keypad

A telephone keypad is a keypad that appears on a "Touch Tone" telephone. It was standardised when the dual-tone multi-frequency system in the new push-button telephone was introduced in the 1960s, which gradually replaced the rotary dial....

, either in a home or mobile phone, there will be the 123-keys at the top. A phone key-pad also has the special buttons labelled * (star

Asterisk

An asterisk is a typographical symbol or glyph. It is so called because it resembles a conventional image of a star. Computer scientists and mathematicians often pronounce it as star...

) and # (octothorpe, number sign

Number sign

Number sign is a name for the symbol #, which is used for a variety of purposes including, in some countries, the designation of a number...

, "pound" or "hash") on either side of the zero key. Most of the keys on a telephone

Telephone

The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...

 also bear letters which have had several auxiliary uses, such as remembering area codes or whole telephone numbers.

The keypad of a calculator

Calculator

An electronic calculator is a small, portable, usually inexpensive electronic device used to perform the basic operations of arithmetic. Modern calculators are more portable than most computers, though most PDAs are comparable in size to handheld calculators.The first solid-state electronic...

 contains the digits 0 through 9, from bottom upwards, together with the four arithmetic

Arithmetic

Arithmetic or arithmetics is the oldest and most elementary branch of mathematics, used by almost everyone, for tasks ranging from simple day-to-day counting to advanced science and business calculations. It involves the study of quantity, especially as the result of combining numbers...

 operations, the decimal point and other more advanced mathematical functions.
Keypads are also a feature of some combination lock

Combination lock

A combination lock is a type of lock in which a sequence of numbers or symbols is used to open the lock. The sequence may be entered using a single rotating dial which interacts with several discs or cams, by using a set of several rotating discs with inscribed numerals which directly interact with...

s. This type of lock is often used on doors, such as that found at the main entrance to some offices.