Is expiation obligatory for one who swears an oath while angry or not intending to swear, and what about past oaths, and what is the "laghw al-yameen" (unintentional oath) mentioned in the Qur'an?

Whoever said, "By Allah, I will do such and such," and then did not do it, has broken his oath and must offer an expiation (kaffarah) for an oath, which is: feeding ten poor persons, or clothing them, or freeing a slave. If he cannot find any of these, then he must fast for three days. As for swearing an oath without intending it as a binding oath, this is considered a 'thoughtless' or 'vain' oath (laghw al-yameen), for which there is no expiation and no sin, based on the Almighty's saying: "Allah will not call you to account for thoughtlessness in your oaths, but He will call you to account for your deliberate oaths."