What is a preposition?

By definition, a preposition is a word used before a noun or pronoun to mark its relation to the rest of the sentence.
Common Prepositions
They refer to movement or placement.
about, above, across, after, against, among, around, at, before,
behind, below, beside, between, by, down, during, for, from, in,
inside, into, near, of, off, on, out, over, through, to, toward,
under, up, with.
Less common prepositions
aboard, along, amid, as, beneath, beyond, but, concerning, considering, despite, except, following, like, minus, next,
onto, opposite, outside, past, per, plus, regarding, round,
save, since, than, till, underneath, unlike, until, upon,
versus, via, within, without.