There are many types of cachexia or rather causes, aka wasting, like diabetes, heart, COPD, AIDS, including cancer cachexia, which is a complex syndrome, with many scenarios, and usually a poor indication of prognosis. There is really no set uniform definition. The 10% unintentional weight loss, as Uptown said, anorexia, weakness are some the signs and symptoms. The type of weight loss is usually adipose tissue, and skeletal muscle.

I lost about 50% of my pretreatment weight in a matter of several weeks wether it was from the septic shock, marasmus, cancer or combination, it took several years to gain half of the weight back, 50lbs, with various type treatments, and I'm still prone to lose weight, and did with another recurrences, about 20%.

This should be discussed with his doctors for a proper diagnosis, cause, possible treatment, if not already done.

Good luck.