A more thorough explanation:

A free city is a political and territorial entity that is independent in principle but does not have the full capacity to act according to general international law. Despite this, it is still considered a subject of international law.

• The city of Hamburg in Germany was a free city from 1815 to 1871.
• The city of Danzig (now Gdańsk) was a free city from 1920 to 1939.

These examples illustrate how a free city is a unique entity that is not quite a country but still has some level of independence and recognition in international law. Hamburg and Danzig were both granted special status as free cities by international treaties, which allowed them to govern themselves to some extent while still being subject to certain international laws and agreements.