OPEC: The Organization of Petroleum Exporting Countries is an international organization. Saudi Arabia is one of its founding members and often plays a major role due to its large oil reserves.
Wahhabism: This is an Islamic doctrine and religious movement founded by Muhammad ibn Abd al-Wahhab. It has been variously described as "ultraconservative", "austere", "fundamentalist", or "puritan(ical)"; it's named after an eighteenth-century preacher and scholar from what is today Saudi Arabia.
Mecca: A city in western Saudi Arabia that’s known as the birthplace of Prophet Muhammad and the faith itself. One of the Five Pillars of Islam requires every Muslim who can do so to perform Hajj i.e., pilgrimage to Mecca at least once in their lifetime.