Zero article

In English grammar, zero article is an occasion in speech or writing where a noun or noun phrase is not preceded by an article (a, an, or the). Also called zero determiners.

In general, zero article is used with proper nouns, mass nouns where the reference is indefinite, and plural count nouns where the reference is indefinite. Also, zero article is generally used with means of transport ("by plane") and common expressions of time and place ("at midnight," "in jail").