Here's why:
* Gerunds are words that are formed from verbs but act as nouns. They usually end in "-ing".
* In this case, "dancing" is derived from the verb "to dance" and is used as a noun:
* "She enjoys dancing." (Dancing is the object of the verb "enjoys").
* "The dancing was beautiful." (Dancing is the subject of the verb "was").
Let me know if you have any other questions!