Wiktionary
alt. (context chiefly US dated English) A popular meal offered at a reduced price, usually in inexpensive eatery and often on a plate divided into compartments for different food items. n. (context chiefly US dated English) A popular meal offered at a reduced price, usually in inexpensive eatery and often on a plate divided into compartments for different food items.
Wikipedia
Blue-plate special or blue plate special is a term used in the United States by restaurants, especially diners and cafes. It refers to a low-priced meal that usually changes daily.
The term was very common from the 1920s through the 1950s. , there are still a few restaurants and diners that offer blue-plate specials under that name, sometimes on blue plates, but it is a vanishing tradition. The phrase itself, however, is still a common American colloquialism.
A web collection of 1930s prose gives this definition: "A Blue Plate Special is a low-priced daily diner special: a main course with all the fixins, a daily combo, a square for two bits."
Usage examples of "blue-plate special".
The blue-plate special will feature turkey, stuffing, cranberries, and all the fixin's for a special price of $4.