A Client is a business that is not focused on web hosting, website design, marketing, or maintenance. Most often, they are small business like junk removal, HVAC, etc., that want to focus on their business, rather than deal with WordPress. For them, WordPress is a means-to-an-end; A way to drive leads to their website and eventually generate income through new sales. Clients are only concerned with making their business profitable.
Resellers and Agencies manage many Clients via Properties.