This is the 7035th most frequent Japanese word.
モーレツ
"モーレツ" means "intense" or "fierce."
In this sentence, 'モーレツ' (mooretsu) describes someone's work ethic as intense or extraordinary.
彼の働きぶりはモーレツである。
His work ethic is fierce.
Here, 'モーレツ' (mooretsu) is used to indicate the intensity with which someone applied themselves to studying.
彼女はモーレツに勉強した結果、試験に合格した。
She studied ferociously and passed the exam.
In this context, 'モーレツ' (mooretsu) conveys the extraordinary energy or activity level of a gathering.