This is the 33rd most frequent Czech word.
není
"Is not" or "there is not."
In this sentence, 'není' negates the predicate that something is the 'correct answer.'
Tohle není správná odpověď.
This is not the correct answer.
Here, 'není' is used to express the absence of the subject 'Marie' in the location implied by 'here.'
Marie tady není.
Marie is not here.
Here, 'není' is used to negate the existence of the condition of being 'for sale' for the subject 'this house'.