Definition

Airspace management means a planning function with the primary objective of maximising the utilisation of available airspace by dynamic time-sharing and, at times, the segregation of airspace among various categories of airspace users on the basis of short-term needs.

Source: Regulation 549/2004

Airspace management. The process by which airspace options are selected and applied to meet the needs of the ATM community. 

Source: ICAO Doc 9854: Global ATM Operational Concept