General terms:
* Grammar: This is the most common and general term, encompassing the rules of syntax, morphology, and phonology.
* Linguistic conventions: This emphasizes the shared agreement about how language should be used.
* Language norms: This focuses on the typical patterns of language use within a particular community.
More specific terms:
* Syntax: Refers to the rules governing sentence structure.
* Morphology: Covers the rules of word formation.
* Phonology: Deals with the sound system of a language.
* Semantics: Focuses on the meaning of words and sentences.
* Pragmatics: Examines how context influences language use.
Less formal terms:
* Language structure: A general term emphasizing the organization of language.
* Language system: Highlighting the interconnectedness of different aspects of language.
* The way we talk: A simple and informal phrase.
The best word to use will depend on the context and the specific aspect of language you are referring to.