Let's illustrate this with the depreciation of a machine used in Department 23 of a manufacturer. The depreciation on that machine is a direct cost for Department 23. It is direct because it is traceable to Department 23 without any allocation.
The depreciation of this same machine will be an indirect cost of the products manufactured with that machine. It is indirect because the depreciation is allocated to the products. Perhaps the machine in Department 23 has depreciation of $50,000 per year (cost of machine of $500,000 divided by 10 years of useful life). The $50,000 of annual depreciation is then assigned or allocated to products based on the number of hours that products use the machine. For example, if the manufacture expects 20,000 machine hours of use in the current year, then it assigns or allocates $2.50 ($50,000/20,000) per machine hour to each product using the machine. If Product #189 requires one hour of this machine's time, Product #189 will have $2.50 as part of its indirect costs. Indirect manufacturing costs are also referred to as manufacturing overhead, factory overhead, or burden.