Why is a proper meal called a "square meal"?

my friend,i am still small and i dont know why they call a proper mealas a square meal.this is really fist time to hear from youas proper meal is called as square meal.from where do you came to know that proper meal is equal to square meal?but i know square meal is a ful balanced nutritios food bar,i came to know fromthe search engines only after your question,so better refer to search engine,so that you can get a nice answer to your question.

Maybe it is a way of saying covering all types of food you are supposed to eat..not sure...