C.O.M. stands for “Customer's Own Material.”
Using COM fabric on a project is purchasing fabric from any source and send it to the manufacturer for upholstery, as an alternative to using the manufacturer's own or “graded-in” fabrics, which often costs less! COM is usually used to preserve design intent or adhere to specific quality standards.
Be sure to check the manufacturer's requirements for fabric, for example – the pattern repeat.
A similar option is COL – Customer's Own Leather.