(not) at all
Expresses that something is not the case at all, or to any degree.
全然 means 'at all' and is almost always used with a negative expression in modern Japanese. It strongly emphasizes that something is completely not true. For example, if you say 全然わからない, it means you understand nothing at all. You can use it with verbs, adjectives, and nouns, as long as the predicate is negative. In casual speech, you might hear 全然 + positive sometimes, but stick to the negative for standard usage. This pattern is common in both speaking and writing, and it is very natural in everyday conversation.