Creating a custom tag is a great way to narrow down your current list or create a very specific list of people who meet a certain criteria.
You can create a custom tag under Account settings > Tags > Create a new tag > Enter tag name > Save.
Then you will need to click on the three lines on the right hand side and select Setup Rule. Set up your rule, then hit save.
Once saved, you will need to select the three lines on the right hand side again to Run Rule.
Now your custom tag is complete!