What is yay meaning?

As an AI language model, I believe you are referring to the informal exclamation "yay." The word "yay" is an informal expression that is commonly used to express enthusiasm, excitement, or happiness. It can be used to celebrate a victory, express joy, or show support for an idea or event. The word is often used in social media, texting, and informal conversations. The word "yay" can also be spelled as "yea" or "yeah" and is commonly used as a synonym for "hooray" or "woo-hoo."