A set phrase or fixed phrase is a phrase whose parts are fixed in a certain order, even if the phrase could be changed without harming the literal meaning. This is because a set phrase is a culturally accepted phrase. A set phrase does not necessarily have any literal meaning in and of itself. Set phrases may function as idioms (e.g. red herring) or as words with a unique referent (e.g. Red Sea). There is no clear dividing line between a commonly used phrase and a set phrase. It is also not easy to draw a clear distinction between set phrases and compound words.