Meaning of beam splitter

beam' split"ter

Pronunciation: [key]
— Optics, Photog. Optics,Photog.
  1. a mirror or prism that divides a beam of light into two parts by reflecting a part of the beam, used in camera range finders.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.