Tag place=city/town in the US

What is the definition of the tag place=city/town/village in the US ? Is it very different from the main definition of the wiki ? Or is it specificaly defined somewhere ?
I’m asking because I found a place in Ontario taggued as “city” with a population of 15k where the wiki says “city” is for 100.000+
http://wiki.openstreetmap.org/wiki/City

Thanks for your help.

Seems like a population tag would be the best way to solve this. Then, since population can be misleading (cities that can annex all their suburbs vs. cities that are hemmed in), come up with a better way of defining how major a city is, for example whether they’re in the center of a metropolitan statistical area. And use city/town/etc for the actual legal status.