What is meant by "al-Wakirah," when does it become obligatory, and what are its conditions?

Al-Wakirah is a meal prepared upon the completion of building a house or similar structure. It is recommended because it falls under the category of feeding people, which is recommended in Islam, based on the Prophet Muhammad’s (peace be upon him) saying: "O people, spread peace, feed the hungry, and pray while people are asleep, and you will enter Paradise in peace." Furthermore, accepting an invitation to it is also recommended.