A glass can be defined as a hard, brittle, transparent, noncrystaline substance produced by fusion of silicates containing soda and lime at very high temperatures.

Pelfy’s definition of a glass is something that breaks easily. For instance, a cup.

Now, Pelfy’s definition of a good glass is something that does not break easily. Even if it breaks, it will still stay intact. Look below:

My sister’s car windscreen

Now, how do you define a good glass?