Sipahi (سپاهی, sipaːhi) were professional cavalrymen deployed by the Seljuks, and later by the Ottoman Empire. Sipahi units included the land grant-holding (timar) provincial timarli sipahi, which constituted most of the army, and the salaried regular kapikulu sipahi, or palace troops. However, the irregular light cavalry akıncı ("raiders") were not considered to be sipahi. The sipahi formed their own distinctive social classes and were rivals to the Janissaries, the élite infantry corps of the Sultans.
A variant of the term "sipahi" was also applied by colonial authorities to several cavalry units serving in the French and Italian colonial armies during the 19th and 20th centuries (see Spahi).
The word is derived from سپاهی, meaning "soldier". The term is also transliterated as spahi and spahee; rendered in other languages as: spahiu in Albanian and Romanian, sepuh (սեպուհ) in Armenian, spahis (Σπαχής) in Greek, spahija or spahiya in Serbo-Croatian, Bulgarian, and Macedonian (Cyrillic: спахија, спахия): in Bengali [sipāhī] "sepoy" (সিপাহী). The Portuguese version is also sipaio (with variants like sipai, cipaio and cipai), but in Spanish it was adapted as cipayo. The word sepoy is derived from the same Persian word sepāhī. In Maldivian, the army's soldiers are referred to as {ސިފައިން} "sifain".
The term refers to all freeborn Ottoman Turkish mounted troops other than akıncı and tribal horsemen in the Ottoman army. The word was used almost synonymously with cavalry. The sipahis formed two distinct types of cavalry: feudal-like, provincial timarlı sipahi (timariots) which consisted most of the Ottoman army, and salaried, regular kapıkulu sipahi (sipahi of the Porte), which constituted the cavalry part of the Ottoman household troops.
The provincial governors, or beys, were rotated every few years, preventing land inheritance. The provinces, or sanjaks, were not all equal since Anatolia and the Balkans were mostly ruled by Turks, while other areas of the empire were more flexible, adhering, somewhat, to local traditions.