"outlier" is a gerneralized term in Statistics and Analysis. (and you thought only geek Engineers and Math majorsbothered with that).
An outlier poll is one that does not run close to the norm of the others. An outlier weather model (like the GFS for Ivan, see http://www.nhc.noaa.gov/text/refresh/MIATCDAT4+shtml/051426.shtml?) is one that is so variant with the rest of the models that it does not make sense.
What folks are saying here is that, with two polls showing a BIG bounce (Times and NewsWEAK) and possibly SurveyUSA, too, and Rasmussen showing a small and shrinking one, that Ras is the 'oulier'.
In a derivative, you can say with certain probability that 95% of all circumstances will be within 2 deviations (+-3/4 % is the deviation). An Outlier is one of the 5%.