很 (hěn) means 'very' or 'quite', and 快 (kuài) means 'fast' or 'quick'. Together, 很快 functions as an adverb meaning 'very fast' or 'very soon', emphasizing speed or short duration. Unlike English, where 'very fast' can modify verbs, nouns, or adjectives, 很快 in Chinese almost always modifies verbs or entire clauses — for example, indicating how quickly an action occurs or how soon something will happen.

This phrase is common in everyday speech and writing, especially when discussing timeframes, reactions, or changes. It often appears before the verb (e.g., 他很快就来了 — 'He arrived very soon') or at the end of a sentence for emphasis. While it literally contains two characters, 很快 is treated as a fixed adverbial unit and should not be split in usage. It carries a neutral, conversational tone — appropriate in both informal and formal contexts, though rarely used in highly technical or literary registers.