What It Means
Peak Margin is the highest of several random margin snapshots the exchange takes of your positions during a single trading day — that snapshot, not the margin you had the moment you placed a trade, is what counts as your real requirement for that day.
How It Works
Clearing corporations take a minimum of four random checks intraday; whichever one shows the highest margin usage becomes your peak margin obligation for the day. SEBI introduced this specifically to stop brokers from handing out intraday leverage far beyond real exchange-mandated margins, phasing it in over 2020–2021: 25% of standard margin required from December 2020, 50% from March 2021, 75% from June 2021, and the full 100% — no extra leverage cushion beyond SPAN+Exposure (F&O) or VaR+ELM (equity) — from September 2021 onward.
Warning
Your account can look fully margined when you place a trade and still get flagged for a shortfall later if one of the day's random snapshots caught you under-margined at some other moment — peak margin is retroactive, not just point-in-time.