Minimum Sector Altitude (MSA) is the lowest altitude that may be used which will give a minimum of 1000 ft / 300 m clearance above all objects located in a radius of 25 nm / 46 km centered on a radio aid, initial approach fix or intermediate fix associated with the approach procedure for that aerodrome.

Note that, whilst it is commonly used as a term applying to all situations, "minimum safe altitude" is not a real term by ICAO's definitions.