Appendix:English uncountable nouns
Nouns which may be used in grammatically uncountable senses. An uncountable noun, also known as a mass noun or non-count noun, typically refers to a substance or an abstraction, is grammatically singular, and is generally not used with indefinite articles (a or an) or numbers. If it is so used, the meaning shifts to mean roughly “a kind of” the underlying substance. Many nouns have both countable and uncountable senses. Nouns' senses are assumed countable unless specifically marked uncountable.
For example, glass, as a substance, is uncountable. We say glass is breakable. A phrase like several glasses in this bottle is made of several glasses means “this bottle is made of several different kinds of glass.” On the other hand, a glass or several glasses normally refers to drinking vessels made of glass, which is a separate, countable sense of glass.