A gerund is a verb that also functions as a noun. For example, one can say one is engaged in the act of writing, but one can also say that what one is doing is a thing called writing. A gerund can be part of the subject of a sentence (“Writing takes a lot of effort”) or part of the object (“I’ve done a lot of writing”).
Most writers generally employ gerunds without difficulty, but one aspect of their use can be confusing: the genitive case.
In the genitive case, the pronoun associated with the gerund takes a different form than it would when associated with the same word used as a verb. For example, when expressing that you listened to some people talking, you would write, “I heard them talking.” However, if you are emphasizing talking as a thing rather than an action, you would write, “I heard their talking.” Or, consider the difference between “They heard it breaking” (breaking is a verb) and “They heard its breaking” (breaking is a gerund).
Writers should also make a distinction with possessive forms of nouns: “The girl shouting awakened her parents” uses shouting as a verb (girl is the subject); in “The girl’s shouting awakened her parents,” however, shouting is a gerund (and shouting, not girl, is the subject).
In many instances, the difference in connotation is insignificant, but whether one employs a simple verb or uses it as a gerund can change the sense of the sentence.