A category is a keyword or phrase that helps you keep track of items so that you can easily find, sort, filter, or group them. Use categories to keep track of different types of items that are related but stored in different folders.
Categories also give you a way to keep track of items without putting them in separate folders. For example, you can keep business and personal tasks in the same task list and use the Business and Personal categories to view the tasks separately.
Outlook supplies a list of categories that you can assign items to, called the Master Category List. You can use this list as it is or add your own categories to it.
Items can be assigned to more than one category.
For more information about categories, see Outlook Help.
Assign a message to a category