A gerund is an –ing word that looks like a verb but acts as a noun.
Look at this sentence: Walking is good exercise.
Walking looks like a verb, but walking is the subject of this sentence, so walking is acting as a noun.
Therefore, walking is a gerund.
Sometimes a gerund is part of a phrase.
Walking around the block is good exercise.
In this sentence, Walking is a gerund, but it is part of a phrase. The entire phrase – Walking around the block – is being used as the subject of the sentence. We call this phrase a gerund phrase.
Here are more examples of a gerund phrase:
I like baking cookies.
The phrase baking cookies is gerund phrase. It is used here as the direct object in this sentence.
I have trouble with opening jars.
The phrase opening jars is a gerund phrase. It is used here as the object of the preposition.
Writing thank-you notes takes lots of time.
The phrase Writing thank-you notes is a gerund phrase. It is used here as the subject of the sentence.
A gerund phrase begins with a gerund (an -ing word that looks like a verb but acts like a noun.) A gerund phrase takes the place of a noun in a sentence, either as the subject of the sentence, as a direct object, or as the object of the preposition.