"OT" stands for One True. "OTP" stands for "One True Pairing" say if HUNHAN was your ultimate pairing, you'd say "HunHan is my OTP C:" OT12 would stand for "One True 12" because every EXO stan should love seeing them together.
I think he's an amazing dancer... there's so much to say about this guy. I think to call him Jongin would be too personal(but since he's not reading this, we will) Kai has a sexy persona once he comes on stage. He transforms from Jongin/the shy guy/ to Kai/the sexy guy/ and he does this by dancing. Dancing is his life, it's what he does best and this is why he's the dancing machine of EXO. because he just doesn't dance, he is dance. I could say so much more ^^ but I'll leave it as that. :)