Glalie's name in japanese is literally ice demon, or ice oni. It could be seen that glalie is supposed to be a freakish monster of the cold. Likewise, is japanese name sounds extremely similar to onigiri, or rice balls. That's right, glalie could be a giant sentient rice ball, or as Brock calls them, jelly filled donuts. It also somewhat looks like it's wearing a hockey mask, and it's head profile is similar to that of a cats, and we all know how much Game Freak loves making Pokemon that resemble cats. The concept of a snowball may have also served as inspiration.
Sourceand my own speculation