It's a french sauce made with egg and herbs and delicious if made from scratch. I have made it once, long before I had a clue about cooking. I don't care for any jarred preparation of it, and therefore only have it when offered at a restaurant. It's very rich, but oh my, is it ever good!!!
In my opinion, it is not dissimilar to Hollandaise. It's sort of tart and creamy.
I bet Phyrie knows how to make it, and probably does it well.
Lynners, I agree that there is a time and place for Bernaise as well as gravy!