sound recorded in the form of a photographic image on cinematograph films
optical sound in American English
noun
Films
sound recorded on and subsequently played back from an optical or photographic soundtrack, as opposed to a magnetic soundtrack
Word origin
[1930–35]This word is first recorded in the period 1930–35. Other words that entered Englishat around the same time include: DNA, acoustic phonetics, hypercorrection, logical positivism, video