Diversion

Diversion is the act of proceeding to an airport other than the planned destination during a flight. Diversions can be caused by weather at the destination, medical emergencies, mechanical problems, fuel concerns, or security threats. It is one of the most consequential operational decisions a crew can make.

Planned diversions use the filed alternate airport
Unplanned diversions to the nearest suitable airport may be required for emergencies
Dispatch and ATC coordinate to provide the best diversion option
Cost of a diversion can range from $10,000 to $500,000+ for large aircraft