Input devices are computer hardware components that are used to feed the computer with data. Any electronic device that you touch, press or click to send data or information into the computer is an input device.
Behind every output by any output device, there is an input device. This means there will be no output without input and all inputs are done with the use of input devices. You have to send music to your computer through input means before you can play, you have to type with the use of a keyboard to create your document, there must be a device to control your computer game, etc. All these are done using particular devices and those devices are called input devices.