from Harvard Magazine, 1996
Kiseh Eliyahu

TENNER REFERS TO  the prophet Elijah's reserved seat at the Passover Seder. There is no chair for Elijah at the Passover Seder. On that night, Elijah must visit every Seder throughout the world. Passing through the room at the speed of light like a will o' the wisp, he is visible only to the most alert child through a slight ripple in the wine contained in the Cup of Elijah that we lay out for him. He certainly has no time to sit down.

The actual Chair of Elijah (kiseh Eliyahu) will be found at the bris, or ritual circumcision. Elijah is present at every Jewish bris, and we set out a chair for him so that he can see that we have not forsaken God's covenant. We hope that he takes the time to sit, to have a glass of wine, and perhaps to receive a tip.