MIDI (Musical Instrument Digital Interface) is the networking software and hardware that allows electronic musical instruments to connect and communicate with computers. MIDI covers everything from the type of cables and plugs to be used, to other musical information such as volume, note durations, pitch bend, and modulation. If you intend to connect your home keyboard to an extra sound module or computer, you need to know that the MIDI Out jack on the keyboard plugs into the MIDI In jack on the other unit, and vice versa. This is the most common error people (even professionals) make when connecting MIDI gear! Much new equipment transmits MIDI data over a USB cable, which simplifies the connection process.