What does beurre noir mean in cooking?

beurre noir means: Tart sauce is made from browned butter and vinegar. (in Cooking Dictionary)

What else does beurre noir mean?

• Sauce for fish that contains brown butter and seasonings such as parsley, vinegar, seasonings, etc. (in Cooking Dictionary)
• Slowly heat butter until the color turns dark brown. (in Merlin Dictionary)