fiber optics noun plural 1.: thin transparent fibers of glass or plastic that are enclosed by material of a lower index of refraction and that transmit light throughout their length by internal reflections ; also : a bundle of such fibers used in an instrument (as for viewing body cavities) 2.singular in construction: the technique of the use of fiber optics • fiber-optic\¦ ̷ ̷ ̷ ̷ ¦ ̷ ̷ ̷ ̷ \adjective