Gerunds are defined as the -ing form of a verb. They have several functions.

1. Used as subjects and complements

Skiing is my favorite sport.

Hiking can be very strenuous.

Seeing is believing

2. Used as objects following prepositions and prepositional expressions

Thanks for tending my children.

The job consists of typing, filing, and answering the phone.

3. Used as objects following certain verbs.*

The children enjoyed watching the parade.

Ms. Terrell avoided paying her taxes until it was too late.

Gerunds can sometimes take objects of their own:

Roland is afraid of making mistakes.

Sandy is considering leaving New York.

*These verbs are commonly followed by gerunds.