Gremiale

A gremiale, sometimes anglicized as gremial, is a square or oblong cloth or apron which a Roman Catholic bishop wears over his lap during certain liturgical ceremonies, in order to protect his pontifical vestments. It is neither blessed or consecrated, and has no symbolic meaning apart from its practical function.
The use of the gremiale is prescribed by the Cæremoniale Episcoporum and historically by the Pontificale, which contain rubrics for the Roman Rite of the Catholic Church. The gremiale is used by a bishop on the following occasions:

during the washing of feet in the Mass of the Lord's Supper
during the anointments in connection with Holy orders
during the consecration of a church or altar
while seated on the Cathedra
during the distribution of blessed candles, palms or ashes

The gremiale is ordinarily made of linen; the gremiale used during a pontifical Mass is made of silk, decorated with a cross in the centre, and trimmed with silk embroidery, in colour corresponding with the colour of the chasuble.
Little is known of its history; apparently its origin dates back to the Late Middle Ages. The Roman Ordo of Gaetano Stefaneschi mention it first ; soon after, it is mentioned in the statutes of John Grandisson of Exeter as early as 1339. In earlier times, its use was not exclusive to bishops but was also available to priests.