An adverb meaning very or extremely; indicates a high degree or intensity.
彼は非常に優秀な学生だ。
He is a very excellent student.
今日は非常に忙しくて、昼ごはんを食べる時間がなかった。
I was extremely busy today and didn't have time to eat lunch.
非常に大きな問題が発生した。
A very serious/large problem has occurred.