It usually stands for the name Jonathan.
Jonathan.
Jon Brion's birth name is Jon Wright Brion.
Jon and Kate stand together for the kids.
Jon Reuning's birth name is Jonathan Reuning.
Jon Vomit's birth name is Worthley, Jon.
Jon Pollak's birth name is Jon Pollak.
Jon Maiullo's birth name is Jon Dickerson.
Jon Jon Snipes's birth name is John Ralph Snipes Jr..
Jon Kellam's birth name is Kellam, Jonathan Mark.
Jon Runyan's birth name is Jon Daniel Runyan.
Jon Trapnell's birth name is Jon Charles Trapnell.
Jon Vickers's birth name is Jon S. Vickers.