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1.
An electronic music device that allows individual notes to be programmed and played back.
Most of the electronic music you hear is "played" using a sequencer.
by SynthBaron November 28, 2003
 
2.
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!

Unlcean fool: ...huh? maybe... :(
by lilwangster May 21, 2011
 
3.
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."
by BB48 October 20, 2005
 
4.
I random music term thingy
I have a sequencer at my house
by Franky the wonderdog July 21, 2003