Anything under 10k per year is low mileage around here in the Midwest. But I agree with everyone that it is a very debatable term. Low mileage on a car driven its entire life in the city is much lower than one that is driven out on open roads most of its life. City miles are just a lot tougher on cars than highway miles are. I do consider my 06 dmax with 90k on the clock low mileage. Mostly because try to find one for sale with less than 150k and let me know how many you find.
I don't consider my vehicles that have 165,000 or more to be low mileage, but you get to decide for yourself if that is low mileage for you.