In Ezekia, a Company refers to any organisation in your database (whether they are deemed a client, a prospect or a target company for sourcing etc). A Client however, is a company that appears on at least one project (i.e. they have been entered on an Assignment, Opportunity, or List). A Company will become a Client automatically when they are added to a project. This distinction is reflected throughout the system, including on the Companies page, where the "Clients" button filters for companies associated with any project.