A software or hardware musical tool that allows you to lay down a sequence of notes over a series of measure(s).
It's commonly abused in conjunction with an arpeggiator by the musically uneducated.
Unclean fool: d00d u hav 2 see wut i jus made in FL studio!
Me: It's not just the same three chords arpeggiated over and over in the sequencer in 4/4 time is it? Please don't tell me the rhythm is just a bass drum playing pure quarter notes!
Someone who uses a music program (Noteworthy Composer, Anvil Studio, etc) to recreate music by ear in MIDI format. Usually taken from video games, movies, or general theme songs.
"Dude, I just found a MIDI of the Ghostbusters theme."
"Heh, I know the sequencer who made that."