In signal processing, a tuned filter is a stage in the processing channel which accepts or rejects signals which are tuned for a specific type.
History
Historically, the concept of tuning was to maintain a specific musical scale. When choruses sing in tune, the music reinforces itself with higher harmonics; aesthetically, the notes are more pleasing to the ear. But when signals are out of tune, dissonance occurs; the effect is most noticeable for musical groups of small children, who have not been trained to sing in tune.
Radio
Tuning became important for the development of radio broadcasts. Stations learned to broadcast at a specific frequency, and to share the bandwidth of the frequency spectrum. Thus radio receivers had to have circuitry to tune to a specific carrier frequency. This was accomplished by creating electronic filters which could accept specific frequency ranges, or tuned filters.
Television and video
The specific techniques for audio broadcasting transferred naturally to television. However, as video techniques became more widespread, the types of tuning went beyond the simple radio and audio frequency ranges, to specific spatial discrimination of spatial frequencies and textures.