Glass or Glass?

So my wife and I had an interesting discussion over the past couple of days, which was regarding the definition of a glass. Yes, a glass, the thing that you use when you want a glass of milk.

You see, it actually started when we got married, whenever I get something to drink, I use a glass. However my wife calls it a cup. She says that anything that is not "glass" is a cup, I say it is a glass.

Of course I also call the other glasses, glass glasses. You know because they are made of glass. You have to be able to discern the difference between the plastic and the glass drinking devises. Therefore I call them "glass glasses".
So this dispute was issued out to our neighbors and friends over the past couple of days. I am trying to find out if there are any other people out there that understand and agree with my point of view.

Are plastic drinking devises called glasses or cups? And I am not talking about those flimsy plastic cups you buy at Sam's Club and get 400 for like $5.00
I am talking about the ones in your cupboard. The ones that everyone uses when they want a glass of milk, juice, or even some water.

Please help me resolve this dispute.