An onomatopoeic adverb meaning doing something relentlessly, strictly, or sharply; can also suggest crisp striking or decisive action.
先輩は新人をびしびし指導して、仕事を早く覚えさせた。
The senior trained the newcomer strictly and had them learn the job quickly.
彼女は無駄を省き、びしびしと決断を下すタイプだ。
She’s the type who cuts out waste and makes decisions decisively.
監督は選手をびしびし叩いて鍛え上げた（比喩的表現）。
The coach pushed the players hard (figurative expression) to train them.