Fairly common at the time video output, providing mirroring for a larger external monitor. Apple even offered such a card themselves according to TIL articles, but third party cards were mor popular. This requires a special monitor which syncs at the Macs video frequency, so don't expect you will be able to plug it into your NTSC TV, even with the proper cable adapters.

It may be working now, but it sure looks like it had a major burn-out at some point.