celebratory banquet; feast
A formal or festive meal held to celebrate a special occasion, such as a wedding, anniversary, or achievement.
After the wedding ceremony, a grand celebratory banquet was held.
His colleagues held a feast to celebrate his promotion.
祝宴 is a banquet held specifically to celebrate something, while 宴 is a more general term for any festive gathering.
Compound of 祝 (しゅく, 'celebration') and 宴 (えん, 'banquet'). The kanji directly convey the meaning of a festive gathering with food.