This is the 727th most frequent Italian word.
grave
Serious, important, severe.
Here, 'grave' is used to describe something critical or serious.
La situazione è grave.
The situation is serious.
In this sentence, 'grave' denotes the intensity or severity of the mistake.
Ha commesso un grave errore.
He made a serious mistake.
In this context, 'grave' refers to something deep or low in pitch.