Tags
Tags add a second dimension to your time entries, letting you slice data across tasks. For example, you might tag entries as "client", "deep work", or "admin" regardless of which task category they belong to.

Applying tags
In the timer's tag field, type to search existing tags or create a new one on the fly. Select as many tags as you like.
Global vs. scoped tags
Tags can be global (available on any entry) or scoped to a specific task (only shown when that task or its children are selected).
You manage tag scope in Organize › Tags.
Filtering by tag
On the Reports page you can filter time data to entries that carry one or more specific tags.
Managing tags
See Task Hierarchy & Tags for creating, editing, and deleting tags, and for setting scope and icons.