What exactly does it mean to have optical neuropathy?

Optic neuropathy : Optic neuropathy is usually a vascular or circulatory problem of the small blood vessels of the optic nerve. An inflammatory condition of blood vessels called vasculitis can also result in optic neuropathy. No matter the cause, optic neuropathy can result in severe vision loss in some, but not all patients.

This means there: Is damage to a nerve (neuropathy), speficicially the optic nerve, the major nerve supplying your eye(s). This can be from a number of things, from vasculitis to decreased blood flow as in the case of diabetic optic neuropathy, which is one of the leading causes of blindness.

Dysfunction of nerve: Optic neuropathy is a generic term for dysfunction of that nerve. It can be due to immunologic problems such as multiple sclerosis, or vascular insult, some inherited diseases, and some spontaneous conditions with no known cause. Most disturb the vision but some are reversible. Others create permanent damage with lowered vision, lowered color sensitivity and loss of blood supply to the nerve.