What is Parent Category under posts

when you create posts they belong to categories. each category can have “child” categories so you could have a post about Ford cars for example and while you could have a menu somewhere that shows all your categories it’s tidier to have them work on a parent/child basis like this:

Cars (parent category)
|- Aston Martin
|- Jaguar
|- Ford (child category)
|- Post A
|- Post B
|- Post C
etc

when you create your post about Ford cars you can tell wordpress that this post is to be stored in the category Ford but also accessible under the parent category or Cars.

hope this helps 😀