All-in is a term that is used only among restauranteurs. Not only is it used only among them, but they try their damnedest to keep the public from learning the term and what it means.
All-in is a dish that you can find on the menus in a great many restaurants spanning the whole gamut of ethnic cuisines, at all price points. To prepare all-in, chefs inventory the supplies of perishable goods in their kitchens, gather up everything that is on the verge of spoiling and concoct a fancy, or sometimes not so fancy, dish out of it all. This allows the restaurant to sell, rather than throw out, these ingredients, thereby improving their profits.
Of course, you will rarely see “all-in” as the name of a dish on a menu. Instead, inexpensive, family-style restaurants will usually call it something like “chef’s special” or “daily special.” High-end, snooty restaurants may give it a name like “succulent mélange” or “luscious bricolage.” However, whatever the name on the menu may be, back in the kitchen they call it all-in and heartily mock the patrons who order it.