[taken from "Sequencing Basics" by Don Muro]
-It might be easier to understand how this process works if you understand a basic difference between a tape recorder and a sequencer. A tape recorder records only the finished product: sound. A sequencer records everything that goes into making the sound but not the sound itself. In other words, the sequencer records the performance information and then on playback "tells" a MIDI-equippped instrument what to do to reproduce the sound. Sequencers make it possible to edit any aspect of performance information. For example, most sequencers allow us to correct wrong notes, to increase or decrease a song's tempo, to play a song back in a different key, and more. A sequencer, therefore, is a device that can record, edit, store, and play back digital data which represent a musical performance.