Aftershave is cologne, it just contains lower levels of the fragrance oils then what you find in most cologne. There are a couple different designations all which convey how much fragrant oil is contained in the product. The more oils, the stronger the scent and the longer it will last (and the more expensive it will be).
Aftershave/Splash
Eau de Cologne
Eau de Toilette
Eau de Parfum
Generally, most men's cologne (especially the mass marketed stuff) will be EdT and lots of women's perfume is EdP.