A Core brick is a frozen tub of leftovers. Freeze in rectangular tubs and they look like bricks (hurt like them if they fall out the freezer too).
Cook a little extra and freeze a brick or 2 for the night you can't be stuffed cooking, or the family is having pizza. Or you just want a hot lunch on a cold day. Really, any of the "wet" dishes brick up nicely like casseroles, soups, curry, pasta etc