It refers to a legendary group of Chinese settlers who went to a faraway corner of China to escape the cruelty of the time. Their new home was referred to as "shih wai tao yuan," a name which later became synonymous with paradise on earth.
傳說中，一群人為了避難而逃到某個偏遠的角落；他們的新家被稱為「世外桃源」，以後就被當作是人間福地的意思。