What is meant by prohibition, and is everything forbidden considered unlawful, and what is the meaning of His — the Almighty’s — saying: (…and what he has forbidden you, refrain from)?

Prohibition (an-nahy) is abstaining and refraining from an action. It comes from a superior to an inferior, and its forms are numerous, including: "Do not do [such and such]," the prohibitive "la" (لا), and "Beware of sitting." The default rule for a شرعي (Shar'i) prohibition is prohibition (tahreem), based on the Almighty's saying: "And whatever the Messenger has given you—take it; and whatever he has forbidden you—refrain from it." A prohibition may indicate disfavor (karahah) or something other than the best (khilaaf al-awla) if there is evidence to divert it from being a prohibition (tahreem), such as drinking while standing. What the Messenger of Allah, may Allah's prayers and peace be upon him, forbade must be avoided, and his prohibition is from the revelation of Allah, the Exalted.