A verb form ending in -ing that functions as a noun.
Here's why:
* Verb form: Gerunds are derived from verbs. They are formed by adding "-ing" to the base form of the verb.
* Function as a noun: While they are derived from verbs, gerunds act like nouns in a sentence. They can be the subject, object, or object of a preposition.
Example:
* Running is my favorite exercise. (Subject)
* I enjoy swimming. (Object)
* I'm tired of waiting. (Object of a preposition)