The definition
Market price, printed as MP, means the dish’s price is not fixed on the menu because it changes with what the restaurant pays for it.
It is used most on seafood, where prices move with the season, the weather, and the catch: lobster, oysters, crab, whole fish. Some steakhouses use it for a large cut like a tomahawk. The restaurant is telling the guest, in two letters, “ask us tonight’s number.”
How you hear it
The question is the whole point of the line. A guest who has to ask, and then does not like the answer, is a guest who feels ambushed. A good server offers the number before being asked.
Where it shows up on the menu or the check
On a printed menu, MP sits where the price would: at the end of the dotted leader, in the price column. Some menus print “market” or “seasonal” instead, and some print the weight (“1½ lb”) with MP so the guest knows what the number is for.
On the check, market price is a real number like any other. The server or the POS enters tonight’s price when the item is rung in. That is where the trouble starts if the number was never said out loud: the first time the guest sees it is on the check.
On a QR menu that you can change from a phone, you have a choice paper does not give you. You can print MP on the table copy and still put tonight’s number on the phone menu, because the hosted menu can change at four o’clock when the delivery comes in.
What it means for prices and printing
Market price exists because reprinting a menu every time an invoice changes is not practical on paper. That is also its cost: guests read MP as “expensive” and some will not order it at all. If the price moves only a few times a season, printing the number and changing it when it moves is often better for sales than MP.
In Gaslamp every item carries a real price, from $1 to $9,999, and there is no MP setting. You have two honest options. Set tonight’s price when the fish comes in and change it when it moves; the menu behind your QR code follows about thirty seconds after you save, and you print a fresh copy for the tables when you want to. Or write “market price” and the weight in the note under the section heading, and let the server quote it.
Whichever you choose, write down who updates the number and when. A market price that is right on Monday and wrong on Saturday is worse than MP.
Where it comes from
The general sense of “market price” is the going price something sells for on the open market; the menu use, where the price depends on the cost of supplies, is recorded in Wiktionary with MP as its abbreviation. We could not find a reliable origin for when menus started printing it.
Go deeper: How to update menu prices without reprinting