A preposition is a word that introduces a prepositional phrase, and often relates to space and time (eg above all expectations, by the way, from outer space, on the run, without a pause).

Early grammarians thought that ending a sentence with a preposition was a grammatical fault to be corrected: Who are you going to the movies with? needed to be rephrased as With whom are you going to the movies?

This is no longer the case. It is not an error to end a sentence with a preposition, but it can sound a little less formal, so check the context of your writing:

The prohibition against ending a sentence with a proposition arose from the use of phrasal verbs.

Phrasal verbs consist of more than 1 word – often a verb plus an adverb or a verb plus a preposition:

When a phrasal verb comes at the end of a sentence, the sentence ends with a word traditionally thought of as a preposition. (When used in this way, the word is referred to as a particle; it is no longer acting as a preposition.) It was thought that prepositions should only be found at the start of a prepositional phrase. Something seemed to be wrong with the sentence, so moving the preposition became a grammatical ‘rule’.

Today, grammarians recognise phrasal verbs, and agree that avoiding having a particle at the end of a sentence is unnecessary, and can lead to unnatural and pedantic constructions. An example is Winston Churchill’s famous quip: This is the type of arrant pedantry up with which I shall not put.