FKK is the German acronym for 'Freikrperkultur' or Free Body Culture simply meaning naturism or nudism.
Nude beaches in Europe are often labeled FKK.
Sometimes you will even see something labeled as an "official" FKK beach, but there is no organization or association called FKK. It literally means only nudism in it's pure form.
In normal use, the acronym has no sexual connotations and should not be confused with FKK adult entertainment clubs in Germany.
The opposite of a FKK beach is a textile beach, simply meaning a beach where people wear bathing suits.
You are almost right there but to make it complete you also have to tell that it started under the regime of Adolf Hitler, he was strongly thinking people and aspecially Arisch people as we know don't be ashamed of there body's and also admired those with the blue eyes and fair hair to make kids, it made THAT part easyer when they met nude and live nude, there where complete nude holiday camps where there was no clothing at all. A walhalla for some of us I imagen.(sorry if I made a spelling mistake but at least I tried)
FKK started a long time before the Nazis appeared, around the turn of the 20th century. The Nazis approach to FKK groups was the same as in most other areas of society; they either banned them, or they co-opted them into party-controlled organisations.