Umm Subwoofers are dedicated bass speakers with very low freq. response in order to reproduce the bass, so you should probably look for ones with frez. response in the 30Hz or 20 Hz. The lower that number goes, the lower the bass it can reproduce, but human ears can hear down to 20Hz.
A woofer is a speaker that can produce bass, but not nearly as much as a sub. Maybe others can explain it better?? I am sure you will notice the difference if you listen to something with the sub on and then turn the sub off, you'll know what I am talking about then.
Of course the best thing to do is to actually go and listen to the speakers before you buy if possible! That's the best way to tell if you will like them or not.