A Berliner Pfannkuchen (referred to as Berliner for short in many regions outside Berlin—especially in the West, but Pfannkuchen inside Berlin—and in many other regions, mostly in the north east of Germany, Kreppel in Hesse, and Krapfen in Bavaria) is a traditional German pastry similar to a doughnut with no central hole, made from sweet yeast dough fried in fat or oil, with a marmalade or jam filling and usually icing, powdered sugar or conventional sugar on top. They are sometimes made with chocolate, champagne, custard, mocha, or advocaat filling, or with no filling at all.
John F. Kennedy's words "Ich bin ein Berliner" are standard German for "I am a Berliner". Mentioned in Len Deighton's 1983 novel Berlin Game, an urban legend has it that due to his use of the indefinite article ein, Berliner is translated as "jelly doughnut", and that the population of Berlin was amused by the supposed mistake. This is incorrect, insofar as when leaving out ein, the meaning only changes slightly (compare I am Berliner and I am a Berliner). The normal convention when stating a nationality or, for instance, saying one is from Berlin, would be to leave out the indefinite article ein. Throughout the 1980s, the legend was spread even by reputable media like The New York Times, The Guardian, BBC and NBC.
However, Kennedy used the indefinite article here correctly to emphasize his relation to Berlin. Additionally, the word Berliner is not used in Berlin to refer to the Berliner Pfannkuchen. These are simply called Pfannkuchen there and therefore no Berliner would mistake Berliner for a doughnut.