Prepositions are connecting words that show the relationship between a noun and the rest of the sentence. There are three types of prepositions: simple prepositions which are one to three syllable words indicating location, direction, or association; compound prepositions which consist of two or more words; and idiomatic expressions which are prepositions used in idioms that take on a different meaning than the individual words. Prepositions are an important part of speech that provide information about how nouns are related to verbs and other parts of a sentence.