Plain meaning
Start with the shortest useful explanation before going deeper.
The simplest and most widely used AMM model, based on the formula x * y = k where x and y are token reserves and k is an invariant. Every swap changes the ratio of reserves while keeping the product constant, producing a hyperbolic price curve. CPMMs provide liquidity across the full price range (0 to infinity) but are less capital-efficient than concentrated liquidity designs. Raydium's standard pools use this model.