Here everyone. Good to be part of this forum!

My professor recently put out an assignment that is heavily based on excel. Part of the assignment requires the use of hat extensions. My professor's exact words we

"label the resulting column with a hat extension. For example, calculate yhat = (y_{t} – y_{t-1})×100 where t is a Quarter. You should now have yhat, chat, ihat, mhat, phat, rhat."

What is a hat extension? What is it used for? How may I use it? I've tried searching all over without finding any answers. Also, it would be great if anyone could point me towards any resource about hat extensions.

Thank you in advance.