What does RACER3 SGF J41 MEM ERLIN5? mean?

This is the course the plane has been cleared for. Racer5 would be a departure procedure - a preplanned route published in the Instrument proceedures for the airport. SGF is the Springfield Vortac, a navigational radio beacon located near Springfield Missouri. J41 is a jet airway - a predefined high altitude route. MEM is the Memphis VORTAC. Erelin5 is as STAR - a standard terminal arrival procedure. This use of pre planned routes cuts down on the amount of instructions ATC must provide the pilot. In this case he pilot would now to follow the plan for the racer5 departure until he reaches Springfield, then to follow J41 to Memphis, and at Memphis to follow Erelin5. Once on Erelin5 ATC will provide the approach procedure to be used to reach the active runway. if you would like to see a STAR procedure chart, use this link: http://204.108.4.16/d-tpp/0804/00026ERLIN.PDF

That's the route of flight. RACER3 is a published departure procedure. SGF is the Springfield, MO VOR (ground navigation station). J41 is a high altitude airway connecting SGF and MEM. MEM is the Memphis, TN VOR. ERLIN5 is a published arrival procedure into Atlanta.