Originally Posted by glennaa11

take a look at the Mileage Run forum here at Flyer Talk
http://www.flyertalk.com/forum/mileage-run-deals-372/

There seem to be a couple of different definitions, either find "cheap" enough fares and just flying a same day round trip just to colect miles.

Or people manage to use the fare rules to go on all sorts of crazy itineraries with multiple connections to accumulate miles for the same fare as a direct flight (or sometimes cheaper than a direct flight). Like going from Miami to New York via LAX, SFO and ORD. Or maybe there's another term for that sort of trip, but mileage run seems to fit it pretty well since you take all of those extra flights just to gather more miles.