What is a 'Popping Crease' and why is it called a 'crease'?

A popping crease is one of a pair of white lines found on a cricket pitch. Without getting too much into the specifics of the game (do you have a few hours/days to spare for a full explanation?), these lines are 4 feet in front of the wicket on each side of the pitch, and serve two main functions (there are others too):
- bowlers must have part of their foot touching the ground behind this line when bowling the ball
- if a batsman does not have part of their body or bat touching the ground between the line and the wicket, they may be run-out or stumped

The term 'crease' was used because originally they were scratched or cut into the pitch. They were up to 1 inch deep and wide. Eventually these cuts were replaced by painted lines that are still used today, but the term 'crease' stuck.

As a bonus answer, the term 'popping' originated from the 'popping hole' that was initially used as a mechanism for running out a batsman. This was quite literally a hole in the ground in front of the wicket that the ball needed to be placed in to run our the batsman.

https://en.wikipedia.org/wiki/Crease_(cricket)
https://www.espncricinfo.com/story/cricket-through-the-ages-101531