What is the definition of fasting linguistically and legally (in Islamic law), what are its pillars and conditions for its validity, is the testimony of one who saw the Ramadan crescent moon alone rejected, and what is the ruling on one who broke their fast during the day in Ramadan under duress; is expiation or a make-up fast required?

Fasting, linguistically: absolute abstinence from something. Islamically: abstaining from things that break the fast with the intention of worship. Its pillars are: the fasting person, the intention, and abstaining from things that break the fast. Conditions for its validity: Islam, and purity from menstrual and postpartum bleeding. Conditions for its obligation: maturity, sanity, capability, and residence. The sighting of the Ramadan crescent is confirmed by a single trustworthy witness. Whoever sights the Ramadan crescent alone is obligated to fast. Whoever is forced to break their fast incurs no sin, but must make up the day.