Inflammation of the veins - it can be quite painful with fever like symptoms.
I had it when I was having problems sorting out my blood pressure medicine - it manifested as a swollen and inflamed left leg and recurred several times. My BP prescription was changed from Beta-Blockers to Ace-Inhibitors and it hasn't recurred.
It is a very generalised term describing an inflammation of blood vessels, mostly arteries of which there are many causes..........probably the commonest being Temporal Arteritis.
Not a very descriptive or helpful term when used in isolation.