A participle that ends in ing. and functions as a noun.?

A participle ending in "-ing" that functions as a noun is called a gerund.

Here are some examples:

* Swimming is my favorite exercise. (The gerund "swimming" is the subject of the sentence.)

* I enjoy reading. (The gerund "reading" is the direct object of the verb "enjoy".)

* She's good at dancing. (The gerund "dancing" is the object of the preposition "at".)

Remember, a gerund will always function as a noun in a sentence, even though it's formed from a verb.