Controlled Airspace is airspace of defined dimensions within which all aircrafts are controlled.

UK Airspace is divided into classes, labelled from A to G. (Although there is currently no class B airspace in use.)

Classes A, B, C, D and E are controlled airspace.

Classes F and G are uncontrolled airspace.

Controlled airspace is subject to restrictions regarding entry and compliance with Air Traffic Control (ATC) instructions.

A Control Area (CTA) established at the confluence of ATS routes in the vicinity of one or more major aerodromes is known as a Terminal Control Area (TMA).

The part of an airspace of defined dimensions above a defined area where flights are not allowed, is called the terminal area.