What are those vertical lines in Notepad++ called? The ones that light up for matching brackets or tags, etc

I'd like an actual term for them. Tab lines?

I can't find a reference to them on google because i don't know what to search for!

I wanna see if there's something like this for Gedit.

What are the lines in Notepad ++ called?

This answer correctly points out that they're "Indent Guides".

How do you make a vertical line in Notepad ++?

In case you are looking for this option in Notepad++ at ~v7. 8, the setting is located near the center of the "Vertical Edge Settings" window under Settings > Preferences > Editing : You can type in one or more numbers (separated by white space) to show one or multiple vertical lines.

What you are probably looking for is called the "Indent Guide".

In Notepad++ 5.9.8 on Windows, it is found under View/Show Symbol/Show Indent Guide.