What is a "contrafactum"?

a. An improvisatory technique used by church singers in Spain and Italy inwhich three voices embroidered the psalm tone, making simple chant soundmore splendid. b. A Christian society of laymen emphasizing religious devotion and charity;performing laude was an essential part of their fraternal life

c. A catch-all word to describe a polyphonic setting of a wide variety of strophicItalian poetry.
d. The transformation of a secular piece of music to a sacred one; occasionallya sacred work is given a secular text.

d