Basically it’s showing that the pages with the dash before each one is a sub-page of the parent one.
Example:
Electronics, Power, and Sensory Systems
– #808 Mini Camera
– Capacitors, Resistors, and Semiconductors
The first one without a dash is the parent, then the ones with the dashes are subpages of that parent. If you look in the column to the right of the items with dashes, it shows the parent they exist in.
So, on the front of your site, I can go to the Electronics, Power, and Sensory Systems page and the URL looks like this:
https://greenbotdynamics.com/electronics
If I go to the Capacitors, Resistors, and Semiconductors page, you will see the URL is now showing that page and the parent page it exists in.
https://greenbotdynamics.com/electronics/capacitors-resistors-and-semiconductors
Basically, this structure in the admin area is how it would look whenever you have pages or categories that contain child pages or categories. It’s a visual display showing which ones are sub-pages or categories of the parent they exist in.
In my site, I have my theme documentation set up with a parent category and sub-categories like this:
Theme Documentation (this is the parent category)
– Set Up Amble (a child sub-category)
– Set Up Definite (another child sub-category)
So it shows the dashes next to the sub categories.