Prepositions in many languages are used with nouns and pronouns to indicate relationships such as direction and position relative to the referents of those nouns and pronouns. Common English prepositions include of, in, from, near; there are around 45 prepositions in English.
In some languages, such as Japanese, the preposition follows the noun, in which case it is called a postposition. In other languages, case endings take the place of some or all prepositions. In Russian, a preposition can be a single consonant (such as 'в', in or to), in which case it functions as a clitic.
According to some prescriptive grammarians, a sentence should not end with a preposition. As with split infinitives, authorities disagree about this rule.
In linguistics, adposition is a catch-all term for both prepositions and postpositions.