A gerund is one of three classes of words called verbals — words based on verbs and expressing an action or a state of being but serving another grammatical function. (The other two are participles and infinitives.) A gerund, which functions as a noun, can consist of a single word or a phrase.
The four types of gerunds and gerund phrases follow:
Gardening is my favorite hobby. (Gardening is normally a verb, but here it is the name of an activity.)
Gardening in the summertime is a challenge because of the heat. (The gerund is followed by a modifying adverbial phrase, forming a gerund phrase.)
2. Direct Object
My neighbors admire my gardening. (The admiration is not for the action of gardening, but for the results of the action.)
I am enjoying my gardening this year. (The direct object of the subject is “my gardening this year.”)
3. Object of Preposition
I have received several awards for my gardening. (The awards have been given for the results of the activity.)
Some people consider my interest in gardening an obsession. (The gerund phrase is “gardening an obsession.”)
4. Subject Complement
My favorite hobby is gardening. (Again, gardening is described as something done, not the act of doing it. The statement is the inverse of the first sentence in this group; here “My favorite hobby” is the subject, and gardening is its complement.)
I do my gardening in the morning. (The phrase “gardening in the morning” is the subject complement.)
Confusion with Present Participle Phrases
If a sentence resembling one of these statements includes a comma, it’s likely to contain a present participle phrase, not a gerund phrase. For example, the sentence “Gardening in the summertime, I built up a resistance to hot weather” contains a present participle phrase, which includes a participle, a verb functioning as an adjective or an adverb.