That can't possibly be a thing
I've heard of Ash Wednesday but I have definitely not heard Pancake Tuesday
At least it sounds a lot more pleasant, I want no ash on my wednesday but I will accept pancakes on my tuesday
Also known as Shrove Tuesday. I think it was a way to use up a bunch of stuff before fasting during Lent. It wasn't a massive thing in my Australian Catholic household growing up, but IIRC sometimes we made a token gesture.