Literally, the "Bath of Mary," it is the original name for the common double boiler used in cooking. The "Mary" in this instance was a Jewish woman who lived in ancient Alexandria and was known to be one of the earliest practitioners of alchemy. It was used to slowly heat substances, a practice necessary for alchemy.
Kitchen Table Tarot: Pull Up a Chair, Shuffle the Cards, and Let’s Talk Tarot
At the time of this writing (late March 2020), I keep thinking about the Wheel. I wonder where we will be on the Wheel when this is posted....