The strike below spot with the largest put open interest; often acts as support.
The put wall is the strike below the current price that holds the largest put open interest. It tends to act as support: dealers who are short those puts buy the underlying as price falls toward the strike to stay hedged, cushioning the decline. Together with the call wall it brackets the market's near-term expected range.
More terms: Gamma wall · Delta neutral · Gamma · 0DTE options · Dealer hedging · Call wall