Line on the right in Intellij Idea code editor

Question

What is that line on the right in Intellij Idea code editor?

Here you can see the line:

Answer 1

That's the right margin. It's telling you roughly how long your lines should be for readability purposes. You can adjust its length in the settings (see the link above), although the default of 80 characters is a widely accepted standard.

Note that if you try to write a line longer than that marker, it may cut the line down and put the remainder on the line below.

Answer 2

The right margin can be toggled in the Editor | Appearance settings:

To change the position of the margin, use the Code Style options:

See help for more details. Basically, it's the guide line showing where the wrapping will occur (if enabled for certain code constructions).