A "square meal" is an expression meaning a full and satisfying meal.
How It's Used
“Snacking used to be a no-no. Three squares a day will satisfy just fine, the common thinking went while eating between meals will ruin your appetite for the scheduled ones.”
—Linda Giuca, “The wrong snacks can scuttle a diet: Americans love their daily extras. Unfortunately, they love them high in fat and high in calories,” The Philadelphia Inquirer, December 30, 1998, p. F6 republished from the Hartford Courant.
"The ravishing Ms. Zeta-Jones looks as though she hasn't had a square meal in years, but that's perfectly OK. The cliché of the super-sized chef should certainly be put to rest if it hasn't already been. But this is a movie about a woman whose life is cooking (not that the filmmakers trouble themselves much to explain her passion), so shouldn't we see Kate do more than decorate a dessert plate or garnish an entrée?”
—Joannne Kaufman, “Film Review: Bland ‘No Reservations’ Is All Kitchen, No Heat,” The Wall Street Journal, July 27, 2007, p. W1.