ETOPS area

An ETOPS area is an area containing airspace within which an ETOPS approved aeroplane remains in excess of the specified flying time in still air (in standard conditions) at the approved one-engine-inoperative cruise speed from an adequate ETOPS route alternate aerodrome.

Source: EU-OPS

See also:
Adequate ETOPS en-route alternate aerodrome
Approved one-engine-inoperative cruise speed
ETOPS (Extended range operations for two engine aeroplanes)
ETOPS area
ETOPS planning minima
Types of ETOPS En-Route Alternates