According to Wikipedia, to eat humble pie, in common usage, is to apologize and face humiliation for a serious error. Humble pie, or umble pie, is also a term for a variety of pastries, originally based on medieval meat tripe pies.
The expression derives from umble pie, which was a pie filled with liver, heart and other offal, especially of cow but often deer or boar. Umble evolved from numble, (after the French nomble) meaning ‘deer’s innards’. Umbles were considered inferior food, in medieval times the pie was often served to lower-class people.
But according to a book I read years ago (I can’t remember the title and its author) the word umble may refer to umbilical cord, as it is also considered inferior food.
If the king and his court could eat prime cuts of meat, the lowly pheasants were only able to eat the internal organs which in turn gave rise to the expression “eating humble pie”. 
I have a question then that keeps bugging my mind: How would you use this idiom in a sentence / conversation?
