Setup: buy the 0.50–0.60 delta put, sell the 0.30–0.40 delta put, 30–60 DTE. Typical use case: a clear bearish thesis on a stock or index, where you want defined risk and don't want to short shares. Pairs well with elevated IV environments — the short put's premium offsets the long put's vega exposure, making the structure more robust to IV changes than a naked long put.
Compare to a bear call credit spread: bear put spread is a debit (pay upfront, profit if stock falls); bear call spread is a credit (collect upfront, profit if stock stays flat or falls). At the same strikes and expiration, both produce identical P&L diagrams — they're synthetically equivalent. Choose based on whether you prefer to pay debit or receive credit, and based on which structure has better fills in the current option chain.