An Organization is a Landing Lion account.
Organization, Workspaces, Collections, and Pages are organized in a hierarchy, where the Organization sits at the top.
Organization > Workspaces > Collections > Pages
Think of an agency as an organization. Every client they bring onto Landing Lion would have a separate Workspace. If anyone in the agency gets added as a user or admin to the Organization, they'll have instant access to every Workspace created under that Organization.
Billing is also done at the Organization level. All Workspaces within an Organization share the page view limits set by the Organization's selected pricing plan, and will also have access to all the same features.