I agree with UNCflyer16's definition of a mileage run. For me a mileage run is any trip I am taking with the primary purpose of getting miles for elite status or a bonus.

I always add as much time as possible to see the place I am flying to as long as the hotel expense doesn't impact the cost too much.

I spent two days seeing Singapore last year on one trip, but my two other trips I had severe time constraints and simply flew in and out on the next flight without even leaving the airport.

My big disappointment was not getting to hang out in some of the places I flew when doing the million mile Latin Pass run. It was simply a matter of having to do the flights over two four-day weekends between work days.
I took quite a bit of heckling from co-workers for traveling to eight countries in South America and Central America and not leaving the airport in half of them. But hey, I can always go back to any of those places now with the 600,000 miles I have left.

There is something about the pure mileage runs when we are simply in the air racking up miles on days off that is hard to get across to others not part of this FT community.