indent

I've just come across this formatting option in Apple Notes. Can anyone clarify what it's called and its purpose? When tapped, it applies a slight indentation to a line of text and adds a small gray vertical line to the left of it.

Today, I noticed a dirt on the edge of the screen of my macbook which cant be removed by cloth. When I inspect in thoroughly, I realized it's not what I expected. It looks like it was punctured, there is an indention. There was probably a small, hard object that got stuck when I close my mac...