Short for infrared beam (which coincidentally doesn't exist) but is intended to refer to either

A: the laser attached to a given firearm

or

B: an infrared sight less likely

often uses in rap songs (Wanksta by 50 Cent or Inf beams by Flatbush Zombies) or in battle rap (Nu Jerzey Twork and others)
"What you know about AK's and AR-15's
equipped with night vision, shell catchers, and inf-beams?"
- 50 Cent, Wanksta
by generic citizen January 17, 2018
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