The Five Pillars of Islam are the five duties expected of every Muslim: shahadah, the profession of faith; salat, ritual prayer performed five times a day; zakat, the alms tax given to benefit the poor and needy; sawm, fasting during the month of Ramadan; and hajj, the pilgrimage to Mecca for those who are financially and physically able.
Britannica notes that the five pillars are especially prominent as an organizing principle in Sunni theology. Shia Muslims also treat these practices as essential but often teach the core of the faith through a different framework, such as the five beliefs (usul al-din) and ten practices (furu al-din) of the Jafari school.
Source: Encyclopaedia Britannica: Pillars of Islam
Image: The Kaaba during Hajj, by Adli Wahid, CC BY-SA 4.0, via Wikimedia Commons.