noun

• (music) Synonym of semitone, half the interval between two notes on a scale.
  "That animals utter musical notes is familiar to every one, as we may daily hear in the singing of birds. It is a more remarkable fact that an ape, one of the Gibbons, produces an exact octave of musical sounds, ascending and descending the scale by half-tones; so that this monkey “alone of brute mammals may be said to sing.”"
• (printing) A picture made by using the process of half-toning.
  "Before leaving New York a handsome booklet had been prepared and printed. The brochure contained the names of the commissioners, their public records, halftone portraits and a carefully prepared statement of the objects of the expedition."
• (art) An intermediate or middle tone in a painting, engraving, photograph, etc.; a middle tint, neither very dark nor very light.
  "“No, I cannot enjoy it,” Cecilia said to Mrs. Devereux; “I don't mind the grey light; cloud and water, and half-tones of colour, are homely English and pleasant, and that opal where the sun should be has a suggestiveness richer than sunlight.[…]”"