Controlled airspace is airspace of defined dimensions within which ATC services are provided. The level of control varies with different classes of airspace.
As per the DESIGNATED AIRSPACE HANDBOOK – Nav Canada
Canadian Domestic Airspace has seven classifications (A, B, C, D, E, F, G). The application of any classification to an airspace structure determines the operating rules, the level of ATC service provided within the structure, and in some
instances, communications and equipment requirements.
Airspace classes A through E are controlled. Class F can be controlled or uncontrolled. Class G is always uncontrolled. Any airspace that is not designated is Class G airspace.