Brinkerl, dabinsky is right, in Romanian a cup is usually made of glass, but in English a cup candy made of glass or plastic and a glass just refers to a cup of made of glass, but in Romanian, if you drink water out of it or juice it is a pahar, and what you drink tea or coffee out of, which is a mug in English is a ceasca, with a U-shaped hat, in Romanian
Louis. A glass is a cup simply because it is meant to hold a drink and that is all a cup is. It is referred to as a cup simply for it's shape (cup also refers to the shape/size of a bra, suction cups, curving your hand to make that shape is "cupping your hand").
A "glass" on the other hand is referring to the material that the cup is made out of. If you asked someone for a glass and they gave you a plastic cup, no one would really blink, but the truth is a plastic cup is not a glass; only a glass cup is a "glass".
If you see the Russel Crowe movie "Master and Commander the Far Side of the World", early in the movie (I think maybe the first scene) you can hear them refer to the telescope as "the glass" when they say "the glass if you please". In the same way, people also call glass cups "glasses".
The handle isn't what makes it a cup. I imagine that in English if someone were to drink coffee out of a cup with a handle on it, even if it were made of glass, it would probably be called a "tea cup" or a "mug" depending on it's size, shape and overall durability... English is confusing I guess, but if you aren't a native speaker, you're doing pretty well! =^)
I know that is what Duolingo would like to suggest, but no. I have spoken Romanian for twelve years and I lived there continuously for two years in three different regions of the country with very few English speaking friends. The word is used for cup and other words are hardly ever used. A glass is a cup but not all cups are glasses. Duolingo ought to correct the mistake.