Usually it's called 'crutching' - the wool is removed from around the tail and the udder, and under the belly of the sheep, to prevent flystrike, to clear the area in ewes for lambs to feed, and to prevent buildup of muck and faeces.
Must be some relationshup to the term used here in the western U.S., called "Tagging"... it's used more for shearing udders of female sheep if weather or other considerations prevent shearing of the ewes before lambing. Often, if the ewe is unshorn, the newborn lamb begins suckling a "tag" of wool near the udder and eventualy starves to death...