These are speech varieties used in specific geographical areas (e.g., Northern vs. Southern Russian dialects).
Informal speech used by specific social groups (youth slang, criminal argot) to create an "in-group" identity. Colloquial Language (Prostorechie)
They often preserve archaic features that the literary language has lost but are typically limited to oral communication among rural populations.
I. R. Galperin distinguishes 5 functional styles: scientific, official, publicist, newspaper, belles-lettres. Корпоративный портал ТПУ LECTURE 13
The informal style used in private, face-to-face communication. Sociolinguistic Significance
This is the highest form of the national language, standardized by grammars and dictionaries.