A gerund is a verb form that ends in “-ing” and functions as a noun in a sentence. For example, in the sentence “Swimming is fun,” the word “swimming” acts as the subject. Gerunds can also be used as objects, such as in “I enjoy reading.” Gerunds can be part of phrases, like “running in the park,” where the entire phrase can serve as a noun. They are often used to express activities or actions, making them useful in everyday language. Understanding gerunds helps improve sentence variety and clarity in writing.