Huehuecoyotl is a word from the language of the Aztecs, who were a group of people who lived a long time ago in what is now Mexico. It means "old coyote" in English.
Now, a coyote is an animal that kind of looks like a dog, but it's wild and lives outside instead of in a house with people.
The Aztecs believed in lots of gods and goddesses, and Huehuecoyotl was one of them. They thought of him as a tricky and mischievous god who liked to play tricks on people.
People would sometimes have parties and dances to honor Huehuecoyotl, where they would dress up in special costumes and masks to look like him. They would also play music and dance to show their appreciation for him.
So, basically, Huehuecoyotl was an old coyote god that the Aztecs thought was funny and liked to celebrate.