Derived from the monumental performances of Michael Phelps, United States swimmer, at the 2008 Beijing Olypic Games for winning eight gold medals, and his 2007 World Championship performance for winning seven gold medals in Melbourne, Australia.
1. Having the characteristics of Michael Phelps
2. Used to describe something that is mind-blowing, unbelievable, record-breaking (mainly this one), incredible, etc. especially a feat.
2. On Guitar Hero, clearing Through the Fire and Flames 100% on Expert is a Phelpsian feat.