Definition of Direct Cost: Direct costs are expenses that can be directly attributed to the production of a specific product or service. This includes raw materials, labor, and any other costs directly associated with manufacturing.

Highly-Customized Computer Part: The customized nature of the computer part makes it a direct cost because it is a specific component needed for the product assembly.

Relevance to Production: Since the part is essential for the assembly of the product, its cost is directly traceable to the product, fitting the definition of a direct cost.

References: Cost accounting literature, such as "Cost Accounting: A Managerial Emphasis" by Charles T. Horngren, defines and discusses the classification of direct costs and their importance in product costing.