expression, godan verb (-ru)
be treated to a meal; be given a meal
Humble expression used when someone else (often a superior or host) provides a meal. The speaker is the recipient of the hospitality.
昨日は部長にご馳走になりました。
Yesterday I was treated to a meal by the department head.
こんなに豪華な料理をご馳走になっ
Thank you very much for treating me to such a splendid meal.