Noun
musica ficta (uncountable)
(music) The use of chromatically altered tones in the contrapuntal music of the 10th to the 16th centuries.
Scholes quotes a keyboard piece by John Bull (1619) which has some similarities to the modern tune, depending on the placing of accidentals which at that time were unwritten in certain cases and left to the discretion of the player (see musica ficta ). Source: Internet
The notational practice of not marking implied accidentals—leaving them to the performer to supply instead—was called musica ficta (i. Source: Internet