as a noun in grammatical terminology, a 'preposition' refers to a word (or group of words) used before a noun, pronoun, or gerund to relate it to another word in the sentence. Prepositions often indicate relationships of place, time, manner, cause, and more.
Prepositions are typically followed by a noun or pronoun, which is called the object of the preposition. Together, the preposition and its object form a prepositional phrase.
In the sentence 'The cat is on the table,' 'on' is a preposition.
'Before the movie starts' contains the preposition 'before.'
She arrived after dinner, where 'after' is a preposition.
It's often advised not to end sentences with prepositions in formal writing, though this 'rule' is more of a stylistic preference than a strict grammatical rule. For example, 'This is the book I was looking for' is considered informal, while 'This is the book for which I was looking' is more formal. Some words can function as both prepositions and adverbs, depending on the context. For instance, 'up' in 'She looked up' (adverb) vs. 'She climbed up the ladder' (preposition). Avoid unnecessary prepositions. For example, 'Where are you at?' is informal and redundant; 'Where are you?' is preferred.