On the heels of aw vs. awe I’ve been asked to discuss yeah vs. yay too. On Facebook, Twitter, and in blog comments, I often see yeah used when yay is meant.
Yeah is the informal version of yes.
Yay is what you say when your boss sends everyone home from work early or your football team gets a touchdown. It is an informal exclamation indicating approval, congratulation, or triumph.
Yay does not mean yeah and yeah does not mean yay. They are not the same and cannot be used interchangeably.