A preposition is a word that shows the relationship between a noun or pronoun and other words in a sentence. It often indicates direction, location, time, or manner. For example, in the sentence "The cat is under the table," the preposition "under" tells us where the cat is in relation to the table. Common prepositions include words like "in," "on," "at," "between," and "with." They help us understand how different elements in a sentence connect. For instance, in "She arrived at noon," the preposition "at" specifies the time when she arrived, giving us a clearer picture of the situation.