A verbal which ends in -ing and is used as a noun called a?

A verbal which ends in -ing and is used as a noun is called a gerund.

Here are some examples:

* Swimming is my favorite exercise.

* Reading helps me relax.

* Cooking can be a fun hobby.

In these sentences, "swimming," "reading," and "cooking" are gerunds because they are verb forms ending in -ing that are acting as the subject of the sentence.