Direct costs can be traced directly to a cost object such as a product or a department. In other words, direct costs do not have to be allocated to a product, department, or other cost object.
For example, if a company produces artisan furniture, the cost of the wood and the cost of the craftsperson are direct costs—they are clearly traceable to the production department and to each item produced—no allocation was needed. On the other hand, the rent of the building that houses the production area, warehouse, and office is not a direct cost of either the production department or the items produced. The rent is an indirect cost—an indirect cost of operating the production department and an indirect cost of crafting the product.
To calculate the total cost of the production department or to calculate each product's total cost, it is necessary to allocate some of the rent (and other indirect costs) to the department and to the product.
I associate indirect with allocation and arbitrary.