On the house
Definition 1 of 1
Pro Tip 1/3Hospitality Gesture
It's often used to show generosity by a business, especially in restaurants and bars. 
After we had dinner, the dessert was on the house as a kind gesture.
Pro Tip 2/3Apology Token
Sometimes used to apologize for a mistake or inconvenience caused by the service provider. 
Our order was late, so the manager made the appetizers on the house.
Pro Tip 3/3Customer Loyalty
Used to reward repeat customers or to encourage them to return. 
Thank you for dining with us often; tonight's meal is on the house!