The path of Sufism starts when a student takes an oath of allegiance with a teacher called Bai'ath or Bay'ah (Arabic word meaning Transaction). After that, the student is called a Murid (Arabic word meaning committed one).
A Pir usually has authorizations to be a teacher for one (or more) Tariqahs (paths). A Tariqah may have more than one Pir at a time. A Pir is accorded that status by his Shaikh by way of Khilafat or Khilafah (Arabic word meaning succession). Khilafat is the process in which a Shaikh identifies one of his disciples as his successor (khalifah). A Pir can have more than one khalifah.