trope

In its simplest form, a trope is a word or phrase added for emphasis or embellishment to an existing text.  The trope evolved into a dramatic dialogue between the cantor and the choir and may have been a precursor to the mystery play.  Most tropes are added to preexisting melismatic passages, while some have a melodic insertion as well as a textual one.

Troping was being practiced by the tenth century, and was employed regularly through the thirteenth century.  At first a few words were added for emphasis, but after a few centuries of this practice, entire poems might be placed between words.  Along with the Ordinary of the Mass, the Benedicamus domino was often troped.  As a result of the Council of Trent, the trope was abolished from Roman Catholic liturgy.

The early motet also used the trope, as it inserts a new text in another voice over the old text.  The sequence may have evolved from a trope to the Alleluia trope.

The sequence is a special kind of trope which was probably originally used in the Alleluia.

English composers, at their extreme, often troped within tropes.