Short answers, pulled from the story.
The term Sunni Islam originates from the word Sunnah, which originally meant the right path followed in pre-Islamic language before becoming a defining political and theological label. The phrase Sunnah began to be used to distinguish loyal community members from heretical teachings during the second Civil War spanning from 680 to 692.
The Sunni identity gained critical political significance following the murder of the third caliph, Uthman, during a time when the Islamic community was fracturing into warring factions. The term was not used as a short form for Sunnis until much later, with some scholars suggesting it was first used by Ibn Taymiyyah and later popularized by Muhammad Rashid Rida in the early twentieth century.
There are four major legal schools within Sunni Islam known as the Hanafi, Hanbali, Maliki, and Shafi'i schools, which represent clearly spelled out methodologies for interpreting Islamic law. The Hanafi school represents reason and is the major tradition in Central Asia, while the Maliki school was particularly important from the ninth to the eleventh century in the Great Mosque of Kairouan.
Most Sunni branches testify to six principal articles of faith known as the six pillars of iman, which are the belief in the Oneness of God, the belief in the Angels of God, the belief in the Books of God, the belief in the Prophets of God, the belief in Resurrection after Death and the Day of Judgment, and the belief in Preordainment or Qadar. These creeds are found in various texts including the confession of the Egyptian Hanafi at-Tahawi and the confession of al-Ghazali.
A study conducted by the Pew Research Center in 2010 and released January 2011 found that there are 1.62 billion Muslims around the world, and it is estimated over 85 to 90 percent are Sunni. This vast majority makes Sunni Islam the largest religious denomination in the world, with significant populations in countries like Indonesia which has the largest population of Muslims in the world.
There is broad agreement that the Sufis are also part of Sunnism, a view that can already be found in the Shafi'ite scholar Abu Mansur al-Baghdadi who died in 1037. All these orders were founded by a major Sunni Islamic saint, and some of the largest and most widespread included the Qadiriyya, the Rifa'iyya, the Chishtiyya, the Shadiliyya, and the Naqshbandiyya.