What does ni chifan le ma mean in Chinese?

"Ni Chifan le ma?" means "Did you eat already?". 'Ni' meaning 'you'; 'chifan' meaning 'eat rice' or 'eat a meal'; 'le' is a past tense particle; 'ma' is a question particle. Some people my also ask 'Ni chi bao le ma?' which means the same thing 'did you eat?'. I was told in class that many Chinese people ask this questions to their guests as a courtesy question. If you have already eaten you may respond 'chi le' or 'chi bao le'. If not 'wo bu chi'.