also: ぜんっぜん
adverb
not at all; not in the slightest
Used with a negative predicate to express complete negation. Standard, neutral register.
その映画は全然面白くなかった。
That movie wasn't interesting at all.
彼の言っていることが全然わからない。
I don't understand what he's saying at all.
adverb
Used with words that have a negative or opposite meaning (e.g., 反対, 違う, 駄目) to mean 'completely'. Not used with ordinary positive adjectives in standard Japanese.
その意見には全然反対です。
I am completely opposed to that opinion.
このケーキは全然駄目だ。
This cake is completely no good.
adverb
Colloquial use with positive statements to mean 'very' or 'extremely'. Common in casual speech, especially among younger speakers. Considered informal.
このラーメン、全然おいしい！
This ramen is really delicious!
全然いいよ、気にしないで。
It's totally fine, don't worry.