Provides a way to categorise contacts by a set of priority groupings; a contact only ever has one category, which is the most important one that applies.
How categories are defined and their priority will depend on your organisation's needs, though a standard scheme(s) is(are) provided to get you started. For example, you might have a way to identify Major Donors, and decide that if someone is a Major Donor, this is the most important category that would apply to them; they may also be One off donors, or Activists or Subscribers or such, but it's helpful to your organisation to prioritise the Major Donor category.
Please see the project repository for fuller examples.