What does God mean by the word "middle" (awsaṭ) in His saying, the Most High: "Its expiation is the feeding of ten poor people from the middle (awsaṭ) of what you feed your own families, or clothing them, or freeing a slave"? And what is its meaning in Islamic law?

The interpretation of verse 89 from Surat Al-Ma'idah explains the expiation for an oath (kaffarat al-yameen), where Allah does not hold one accountable for unintentional oaths (laghw al-ayman), but rather for deliberate oaths (al-ayman al-ma'qudah). The expiation is by feeding ten poor persons with an average (awsat) of what one feeds their own family, or clothing them, or freeing a slave. This is a matter of choice. For whoever cannot find means, then it is fasting for three days. The word "awsat" (average) means the middle ground, meaning the food should not be too expensive nor too cheap, but moderate.