A preposition is a word that links nouns, pronouns, or phrases to other words in a sentence, often indicating relationships in time, place, direction, or manner. Common examples include "in," "on," "at," "between," and "during." Prepositions are typically followed by a noun or pronoun, forming a prepositional phrase that provides additional context. For instance, in the phrase "on the table," "on" is the preposition that shows the relationship between the object and the location.