Chinese nouns do not have articles, such as "the" and "a" in English, nor do they have a plural form.

So the word 大学 (dà xué) can be any of the following meaning:

a university
the university
the universities
universities

The context usually makes clear which is meant. There are however ways to stress what is meant:

一所大学 (yī suǒ dà xué) - Literal: one [measure word,量词] university - One university
这些/那些 大学 (zhè xiē/nà xiē dà xué) - these/those universities