Answer:
 the amount an additional worker adds to the firm's total output. 
Step-by-step explanation:
The marginal product of an input is the change in total output as a result of the change in output by 1 unit 
 
For example, the table below is the total product of labour 
 
amount of labour output 
 
1 10 
 
2 20 
 
3 40 
 
the marginal product of the 3rd worker = (40 - 20) / (3 - 2) = 20 
 
marginal product of the second worker = (20 - 10) / (2 -1 ) = 10 
 
Average output = total output / labour