The ratio of put option to call option trading volume (or open interest) — a sentiment gauge for options traders.
PCR divides the volume (or open interest) of put options by call options for a given underlying, usually the Nifty. A PCR meaningfully above 1 means traders are buying more puts (bearish bets / hedges) than calls; a PCR well below 1 suggests more bullish positioning via calls.
PCR is a sentiment and positioning indicator, not a price predictor — extremely high or low readings are sometimes read as contrarian signals (excessive bearishness can precede a bounce, and vice versa), but it's most useful alongside other signals, not alone.