"A MIDI keyboard is a piano-style digital keyboard device used for sending MIDI signals or commands to other devices connected to the same interface as the keyboard. MIDI is an acronym for Musical Instrument Digital Interface (protocol). The basic MIDI keyboard does not produce sound. Instead, MIDI information is sent to an electronic module capable of reproducing an array of digital sounds or samples that resemble traditional analog musical instruments. These samples are also referred to as voices.
An encoding scheme is used to map a MIDI value to a specific instrument sample. Also, other sound parameters such as note volume and attack are included in the MIDI scheme. The keyboard merely acts as a MIDI controller of sound modules and other MIDI devices, including DAW software.
MIDI keyboards are a very common feature of a recording studio, and any DAW setup. Most include a transpose function and the ability to set different octaves. Many MIDI keyboards have pitch bend and modulation wheels. Some also have extra sets of assignable rotary knobs and/or buttons for sending custom MIDI messages to the synthesiser, sampler or DAW software.
Other features that some MIDI keyboards might include are:
Input for foot switch (usually used as a sustain pedal)
Input for a foot expression controller
Semi-weighted or fully weighted keys
Capability of sending aftertouch
Direct USB connection for use with computers
MIDI keyboards come in a large range of sizes, from 2-octaves to full 88-key length. MIDI keyboards with less than 61 keys tend not to have weighted keys."