Woodworm is not a particular type of creature. It is in fact the larval stage of certain beetles' lives. However in general, or slang, the term is used to describe a variety of wood boring insects that infest timber, creating all sorts of nightmares for home owners.
Woodworm can be difficult to spot, but if left untreated it will cause severe structural damage to a property. It is recommended you contact an expert if you suspect it.