A gerund is a verb form ending in –ing that is used as a noun.
Examples: Skiing is my favorite sport. [subject of the verb is]
My hobby is fishing. [predicate nominative identifying the subject hobby]
Sam enjoys rock climbing. [direct object of the verb enjoy]
We should give snorkeling a try. [indirect object of the verb should give]
Saul has shown great interest in skating. [object of the preposition in]
Do not confuse a gerund with a present participle used as part of a verb phrase or as an adjective.
Examples: The rabbit was sitting by the edge of the running stream. [Sitting is part of the verb phrase was sitting. Running is a participle modifying stream.]