Flughafen vs. Flugplatz
While both German words Flughafen and Flugplatz can be translated as airport, they are not interchangeable. The difference lies in their size, infrastructure, and the type of air traffic they handle, much like the difference between an airport and an airfield in English.
Flughafen
A1A Flughafen is a large, official airport that handles commercial, scheduled air traffic for passengers and cargo. It features extensive infrastructure such as long, paved runways, multiple terminals, customs and border control, and an air traffic control tower. It's the term for major national and international airports.
Wir fliegen nächste Woche vom Flughafen München nach Rom.
(We are flying from Munich Airport to Rome next week.)
Der neue internationale Flughafen hat drei Terminals.
(The new international airport has three terminals.)
Nach der Landung mussten wir am Flughafen durch die Passkontrolle.
(After landing, we had to go through passport control at the airport.)
Der Frachtverkehr am Flughafen Frankfurt ist enorm.
(The cargo traffic at Frankfurt Airport is enormous.)
Wegen des Streiks wurden am Flughafen alle Flüge gestrichen.
(Due to the strike, all flights at the airport were cancelled.)
Flugplatz
B1A Flugplatz is a more general term for any location where aircraft can take off and land, best translated as an airfield or aerodrome. This includes small regional airports, but also fields for private planes, sport aviation, gliding, flight schools, and helicopters. A Flugplatz typically has much simpler facilities and may not even have a paved runway or a control tower.
Am Wochenende gehe ich auf dem örtlichen Flugplatz segelfliegen.
(On the weekend, I go gliding at the local airfield.)
Der Unternehmer landete mit seinem Privatjet auf dem kleinen Flugplatz in der Nähe seiner Firma.
(The entrepreneur landed his private jet at the small airfield near his company.)
Dieser Flugplatz hat nur eine Graspiste für Leichtflugzeuge.
(This airfield only has a grass runway for light aircraft.)
Die Flugschule befindet sich direkt am Flugplatz.
(The flight school is located right at the aerodrome.)
Der Rettungshubschrauber startet von einem speziellen Flugplatz am Krankenhaus.
(The rescue helicopter takes off from a special helipad at the hospital.)
Summary
In summary, the core distinction is one of scale and official capacity. A Flughafen is a large, commercial airport with the infrastructure for international travel and cargo (like JFK or London Heathrow). A Flugplatz is a broader term for any airfield, which is often small and used for general aviation, sports, or private planes. Essentially, every Flughafen is a type of Flugplatz, but most Flugplätze are not big enough to be called a Flughafen.