Tagging your domains is a great way to categorise and help manage filtering by them in the future, for example, if you have hundreds of domains in your account, then adding tags to your domains will help you filter by them later on.
When you add a domain to the system, you can optionally specify up-to 5 tags for the domain, these tags can either be completely custom, or, you can simply choose from some of our pre-defined tags.
When it comes to needing to filter by your tagged domains, you can specify a search qualifier called tags:
in the search input on the domains page.
This qualifier accepts a comma separated list of tags that you'd like to search by.
Here's some examples:
tags:internal,external
tags:my website