purpureus pannus

purple patch

An over-written passage in which the writer has strained too hard to achieve an impressive effect, by elaborate figures or other means. The phrase (Latin, purpureus pannus) was first used by the Roman poet Horace in his Ars Poetica (c.20 bce) to denote an irrelevant and excessively ornate passage; the sense of irrelevance is normally absent in modern usage, although such passages are usually incongruous. By extension, ‘purple prose’ is lavishly figurative, rhythmic, or otherwise overwrought. See also bombast, fustian.

-- The Oxford Dictionary of Literary Terms