Working with Outlook
Categories are key words or phrases that you can associate with Outlook items (messages, appointments, contacts, tasks, journal entries, and notes).
Use categories to create associations between different types of Outlook items, such as messages, contacts, and tasks relating to a specific project, which will necessarily be stored in different folders.
Use categories to create associations between similar items, such as messages, stored in different folders.
Use categories to create associations between similar items stored in the same folder. Keep all your notes, for example, in one folder, but use categories to distinguish one set of notes from another.
Using categories makes it easy to find related items stored in different folders. When you store related items in the same folder, you can easily sort, filter, or group them by category.