Just as a hoover is the colloquial name for a vacuum cleaner, so too nowadays is coving used to describe any form of cornice. The commercial success of the ubiquitous concave paper coated plaster strips sold by DIY supermarkets and builders merchants has commonly lead to all cornice nowadays being referred to as coving.
As language evolves we understand and accept this change in usage and so too do most craftsmen in the decorative plasterwork industry. Just type plaster coving into Google and you’ll get a list of 'traditional' firms who insist they are selling cornice, but on their websites they always make sure they get noticed for selling plaster coving as well.
Originally coving referred to the profile shape of cornice that had a concave moulding. Technically it is known as Cavetto and typically represents a quarter of a circle. Imaginatively it can be visualised as how a bay, like for example Lulworth Cove, appears on a map. It became popular in the UK during the 1930s and remains widely used to this day. So much so that it has become the common name for any decorative moulding that is sold in strips and is designed to cover the gap between the top of the wall in a room and the ceiling.
If we were going to be pedantic we would insist that our business is supplying plaster cornice some of which is actually known as coving. However, we understand modern English so if you come to us looking for egg and dart coving we know exactly what you mean. Just as if you want to clean the carpet you’ll need a hoover!