What is a gerund?

A gerund is defined as a verb form that ends in -ing and functions as a noun within a sentence. This means that gerunds can act as subjects, direct objects, or objects of prepositions. For example, in the sentence "Running is fun," "running" is a gerund serving as the subject of the sentence.

The correct answer highlights this unique characteristic of gerunds, emphasizing their role not only as derivatives of verbs but also in how they can fulfill the functions typically associated with nouns. The focus on the -ing ending as a critical component of a gerund is vital for identification and understanding in the context of grammatical structure.

This definition clarifies why other possibilities do not apply. A verb form that expresses tense relates more to finite verbs rather than to gerunds. A noun formed from an adjective describes a different grammatical transformation, which isn't relevant to gerunds. Similarly, a type of inferential phrase does not pertain to gerunds, as it suggests a different grammatical concept altogether.