Step 1: Define Sufis:
Sufis were Muslim mystics who emphasised a direct, personal, loving relationship with God over ritualistic orthodoxy, seeking spiritual union through devotion, asceticism and love.
Step 2: Origins:
Sufism developed within Islam from around the 8th-9th centuries CE, initially as an ascetic reaction to the growing wealth and worldliness of the Umayyad and Abbasid courts.
Step 3: Organisation into silsilahs:
By the 12th century, Sufism organised into various orders (silsilahs), each following a chain of teacher-disciple (pir-murid) succession, such as the Chishti, Suhrawardi, Qadiri and Naqshbandi orders.
Step 4: Development in India:
The Chishti order, introduced by Khwaja Moinuddin Chishti at Ajmer in the late 12th century, became the most influential in India, followed by saints like Nizamuddin Auliya and Nasiruddin Chiragh-i-Dehli, running khanqahs (hospices) open to people of all faiths.
Step 5: Practices and impact:
Sufi practice included sama (spiritual music), dhikr (remembrance of God), langar (community kitchen) and tolerance of local customs, fostering a syncretic culture that interacted closely with the Bhakti movement and helped shape a shared devotional Hindu-Muslim culture in medieval India.
Final Answer:
\[ \boxed{\text{Sufis: Islamic mystics seeking personal union with God; developed through silsilahs like the Chishti order, which flourished in India via khanqahs open to all}} \]