Interchangeable parts are components that are made to be identical, allowing them to fit into any assembly of the same type. This concept revolutionized manufacturing by enabling mass production, as parts could be easily replaced without needing custom fitting. The idea of interchangeable parts was popularized by Eli Whitney in the early 19th century, particularly in the production of firearms. This innovation not only improved efficiency but also reduced costs and simplified repairs, leading to the development of modern assembly lines and manufacturing processes.