A keypad module is a set of buttons arranged in a block or “pad” which bear digits, symbols or alphabetical letters. Pads mostly containing numbers are called a numeric keypad.
The 4 x 4 matrix keypad usually is used as input in a project. It has 16 keys in total, which means the same input values. It is ultra-thin, easy to interface with any microcontroller and has an adhesive backing for easy mounting for a variety of applications.