"Producer's Surplus is a convenient name for the genus of which the rent of land is the leading species"

Alfred Marshall's quote is describing the principle of Producer's Surplus, which is the distinction between the amount of money a manufacturer receives for a great or service and the amount of cash it costs to produce it. Simply put, it is the extra money a producer makes from selling an excellent or service. Marshall is stating that Producer's Surplus is a broad concept, and that the rent of land is the most popular example of it. This is due to the fact that when a landowner rents their land to a renter, the renter pays the landowner a certain quantity of cash for the right to use the land. The distinction between the quantity of cash the landowner gets and the amount of cash it costs them to keep the land is the Producer's Surplus. Marshall's quote is stressing the significance of Producer's Surplus and how it is a key consider the production of goods and services.