Zero article

It means there isn't an article used before the noun.

No 'a' or 'an' or 'the'.

One night at dinner, she said she preferred the company of her cats to any of the men there. "Though they are like my cats," she went on,"I'd bet you they would like to lurk under bushes or climb up high in trees."

(No 'a' before 'dinner'.)
(No 'the' before 'bushes' and 'trees'. )

Joe(meow)Nation

What Joe(good grammar)Nation is saying is that articles are not always necessary when it's understood. "Lurk under (the) bushes or ....high in (the) trees."

Zero article refers to an occasion in speech or writing where a noun or noun phrase is not preceded by an article (a, an, or the).

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

We have now in this modern instances where using any article would be awkward as when the politician said he "had used THE Google to look something up."

Joe(I am speaking to you tonight through the tubes of the Internet.)Nation