A method of graphically displaying MIDI note data, used by DAW and sequencer software. In this method of notation, notes are graphically displayed as bars on a grid, with increasing time going to the right on the X axis, and increasing pitch going upwards on the Y axis. The left edge of a note bar indicates the "on" time for that note, and the length of the bar represents the duration. (This is where the name comes from -- the pattern of note bars resembles the holes punched in old paper player-piano rolls, which caused the player piano to play notes specified by the holes.)
Typically the software divides the grid into bars and beats according to the time signature in use, so that alignment of the notes with the beats (see quantization) can be easily seen. Notes can be dragged around the grid individually with the mouse, or grouped into selections. Additional data may be represented as points or drawn lines, such as MIDI program change and pitch bend messages.
This notation came into use in the early 1990s primarily because it corresponds to the way MIDI note data works and is represented internally by the software. This, and the fact that it is much less complicated than traditional music drawn on the staff, makes the notation easy for software to draw. However, some electronic musicians also found it easier to read than music on the staff, and actually prefer it to traditional notation.