Diminishing marginal product

Diminishing marginal product is a characteristic of a production function whereby the marginal product of a factor falls as the amount of the factor increases while all other factors are held constant.

Definition

According to Macroeconomics by Mankiw (7th edition),

Diminishing marginal product. A characteristic of a production function whereby the marginal product of a factor falls as the amount of the factor increases while all other factors are held constant.