Hardmode is kind of a dumb term
I mean, yes, it's harder then the first phase, but that's also true of the next phases and there are more defining features than just being harder. plus, it's easy to confuse with hardcore. maybe we should call it the "souls" phase, "hallowed" phase, or just "post-WoF"
each phase kinda corresponds with an update
Early Game = 1.0
Hallowed = 1.1
Post-Plantera = 1.2
Lunar = 1.3