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2.
A product which is of incredibly low quality compared to its nearest competitors, yet maintains a similar price. The term originated from the tendency of such product to utilize colorful flashing lights (possibly in alternating or multiple colors) as a selling point.
Have you seen those cheap-ish third party controllers? Nothing but disco lights, they don't even have all the right buttons!

I got a new mouse, but it went bad after like a month. Stupid disco lights.

Sure this flash drive doesn't have the storage space or the lifespan as that other brand, but it lights up in blue, red, and green! I need some DISCO LIGHTS!

Man, fuck quality, I'm gonna buy some disco lights!
by Kardas W. Fox March 18, 2010
 
1.
The flashing lights on emergency vehicles which, when turned on, signal other cars to get out of the way. This term is most commonly used to refer to such lights on police cars, although it could be used for the same type of lights on ambulances or fire department vehicles.
So I was driving home, not noticing how fast I was going, and suddenly I saw those disco lights in my rear view mirror!
by LateBlt January 30, 2007