Source: Image of gears, public domain, http://www.clker.com/clipart-2950.html; All Graphs by Justin Tapp
Total output divided by quantity of inputs. Should be the average product of labor, or average product of capital.
The marginal product of capital/labor will begin to fall at some point, holding all else constant.
The output produced when we add one additional unit of input.
Additional output generated by adding one more unit of capital.
Additional output generated by adding one more unit of labor.
Additional sales revenue received from employing another unit of labor/capital.
Quantity of goods/services produced.