A MIDI step sequencer is a type of music software that allows you to create and edit sequences of MIDI notes. It's like having a miniature piano keyboard in front of you, with each key representing a different note. You can then drag and drop these notes to create your sequence. A MIDI step sequencer is excellent for creating drum patterns, basslines, and melodies. You can also use it to create chord progressions and even entire songs. Some sequencers even come with built-in effects so that you can add reverb, delay, or distortion to your sequences.