Charm

Charm is a second-order Greek that tells you how delta drifts as the clock ticks, holding price constant. An out-of-the-money option's delta bleeds toward zero as expiry approaches, while an in-the-money option's delta marches toward 1 — charm captures that daily drift.

On NSE weekly expiries, charm becomes significant in the last day or two: a delta-hedged book can quietly become unbalanced overnight simply because time has passed. Professional option desks re-hedge for charm near expiry; most retail traders never measure it directly but feel its effect.