Anything described as Panhellenic has something to do with the country of Greece. The Olympics was originally just one of four Panhellenic sporting events regularly held by ancient Greeks.
The term Panhellenic, not surprisingly, comes from Greek roots. Pan- means "all," and Hellenic, or "Greek," comes from Hellen, "a Greek." So when something is Panhellenic, it's connected to all of Greece or all Greek people. The most well-known Panhellenic poet is Homer. You may also encounter this word in connection with an American college fraternity or sorority: "My mom still stays in touch with her Panhellenic sisters."