Meaning of scanning disk

scan'ning disk"

Pronunciation: [key]
— Television. Television.
  1. (in mechanical scanning) a disk with a line of holes spiraling in from its edge, rotated in front of a surface so as to expose a small segment as each hole passes before it for transmitting or reproducing a picture.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.