What does "sclerosis" mean in medical terms like "multiple sclerosis"?

Sclerosis means abnormal hardening of tissue, from sclero meaning hard and osis meaning condition. Multiple sclerosis, or MS, is an autoimmune disease where the immune system attacks the myelin sheath, the protective covering of nerve fibers in the brain and spinal cord, causing multiple areas of hardened scar tissue. This disrupts nerve signal transmission, causing symptoms like numbness, weakness, vision problems, and coordination difficulties.