Green’s Dictionary of Slang

Apple n.

[abbr. Big Apple n.]

1. [1930s–50s] (US black) Harlem, NYC.

2. [1940s] (US black) a large Northern city.

3. [1940s–50s] the earth, the universe.

4. [1940s+] (orig. US jazz) usu. the Apple, New York City.