Direct costs can be tied to specific products. The most obvious examples are direct labour and direct materials. Thus we can allocate exactly the cost of bought-in parts to the products into which they are built.
Indirect costs are whatever is left over after direct costs have been allocated. Indirect costs are also called ‘overheads’, and include everything from the managing director’s salary to the rent rates paid for the distribution centre – anything that cannot be allocated directly to a given product.