You can give any Pen or Project up to five tags. Here’s an example of adding them to a Pen under Pen Settings > Pen Details.
Tags have global, shared pages. For example, here’s the URL for the tag “dailyui”:
Anybody can see that page. If you tag a Pen “dailyui”, it will show up there. If someone else saves a Pen with the tag “dailyui”, it will show up there too.
You can view a list of all the tags you’ve used on your profile. Here’s an example.
All those tags are links, which allow you to view tagged Pens of just one person (including yourself). For example:
There is also a way to browse by your own tags in Your Work. Start typing a tag in the “Tag” field and you can choose your tag from the dropdown.
On public tag pages, your private Pens will not appear there. But if you’re looking at your own work, private Pens will appear there.