formation constant

For a mononuclear binary complex, if a central atom (central group) M (the 'metal') and a ligand L have been defined, then in the following expressions K n is the stepwise formation constant, and β n is the cumulative formation constant for the complex MLn. They can both be referred to as stability constants (stepwise and cumulative).
K n = K ( ML n − 1 + L ⇌ ML n )
β n = K ( M + n L ⇌ ML n )
Orange Book, p. 11