the.com/square meal

means A full, satisfying, nutritionally solid meal — the kind that properly fills you up rather than just tiding you over.

from The popular story claims British naval ships served meals on square wooden plates or trays, so sailors eating a proper hot meal were literally eating 'off the square' — hence a 'square meal.' It's a vivid tale, but etymologists find no solid evidence for it. More likely, 'square' here draws on its older sense of 'honest, solid, satisfactory, fair and proper' — the same sense in phrases like 'square deal' or 'fair and square.' A square meal, then, is simply one that's properly, honestly substantial — the naval tray story is probably a tasty but false embellishment that stuck.