The clothes you go hiking in are like portable shelter, your first line of defense against the elements -- not to mention your best chance at staying comfortable, no matter what nature throws at you. The very best layers are weatherproof, which means they're both waterproof and windproof.
(Sorry -- zombieproofing is not yet an option. Maybe one day!)
There's a pretty big difference between being proof against the elements or just resisting them, so if a garment is just water- and wind-resistant, I'd call it weather-resistant -- not weatherproof.
Ideally, high-end weatherproof garments will be breathable too. But weatherproofness and breathability, in particular waterproofing and breathability, are always a tradeoff. Today's breathable fabrics are getting more and more waterproof, but they're still permeable on some level.
The good news is that most of us won't ever be out in conditions that would test the really high-end stuff's weatherproofing; but low-end "weatherproof" gear really isn't that proof against wind and rain -- yet another reason why it's worth saving up to buy quality gear. (And checking the usual subjects for great deals.)
Any "outerwear" garment -- jacket, pants, hat and gloves -- can be weatherproof.
My weatherproof shell keeps me warm and dry, even in the worst weather.