I feel the name casual has been used a lot incorrectly. It doesn't mean someone who is bad at the game, or someone who has less play-time. I consider myself a casual player. I like to do things like World Explorer, or waste hours trying to get a cooler looking mount, just for the sake of having a cooler looking mount. I'll even just fly to Howling Fjord or Nagrand just to look around. Casual means 'without serious intentions'. Although I do raid/ run heroics/ PvP a bit, I prefer to spend most of my time doing essentially useless things. But I love it! Also, the name Casual has often been used as an insult, which I feel that it is preposterous to insult someone over how they prefer to play a video game.
Yes, I just spewed my thoughts after browsing the forums, I have no coherent structure to my post, but whatever.
TL;DR -- Casual =/= baddie or someone who plays less.