Sipahi (Ottoman Turkish: سپاهی sipâhi, Turkish pronunciation: [sipaːhi]) were two types of Ottoman cavalry corps, including the fief-holding provincial timarli sipahi, which constituted most of the army, and the regular kapikulu sipahi, palace troops. Other types of cavalry which were not regarded sipahi were the irregular akıncı ("raiders"). The sipahi formed their own distinctive social classes, and were notably in rivalry with the Janissaries, the elite corps of the Sultan.
It was also the title given 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 Persian sepāhī (سپاهی,), meaning "soldier". The term is also transliterated as spahi and spahee; rendered in other languages as: spahiu (in Albanian and Romanian ), spahis (Σπαχής, in Greek), spahija or spahiya (in Serbian, Bulgarian and Macedonian; Cyrillic спахија, спахия). The word "sepoy" is derived from the same Persian word sepāhī.
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.