It is.

https://en.wikipedia.org/wiki/Grammar

In linguistics, a grammar is the set of rules for how a natural language is structured, as demonstrated by its speakers or writers. Grammar rules may concern the use of clauses, phrases, and words. The term may also refer to the study of such rules, a subject that includes phonology, morphology, and syntax, together with phonetics, semantics, and pragmatics.

“everything to do with a nebulous idea of understanding.”

What do you think language is?