Cupeño is the language spoken by the Cupeño people, a Native American tribe that lived in California. It's a way of communicating with others using special words that only people who know Cupeño can understand. It's like having your own secret language that only you and your friends can speak.
Cupeño is a little bit like English, the language you speak every day. In English, we use letters of the alphabet to make words that have different meanings. In Cupeño, they also use words, but they look and sound different from English words.
Since the Cupeño people no longer have their own land, the number of people who speak Cupeño is very small. But some people are still trying to learn and study it so that it doesn't fade away completely.