Phrases There are two kinds of phrases. One is the kind we memorize when we study a language. It is a group of words that have a special meaning together Two phrases that students of English often learn are "keep in touch" and "raining cats and dogs". This kind of phrase is also called an idiom or a fixed expression. The other kind of phrase is a group of words with a certain structure. The words can be changed, and so can the meaning, but the structur stays the same. This kind of phrase is also called a grammatical phrase. The idioms "keep in touch" and "raining cats and dogs" are verb phrases Jf change the words "to sleep under trees" and "eating fish and chips", the phrases are no longer idioms, because they do not have special meanings, bu they are still grammatical phrases, because they have a certain structure. It is useful to know the differences between these two kinds of phrases.