The largest Ottoman administrative unit was the eyalet. Eyalets were provincial territories governed by officials such as beylerbeys, and the term became standard in the late 16th century, replacing the earlier term beylerbeylik.
An eyalet was divided into smaller districts called sanjaks or livas. These districts were administered by sanjak-beys and formed the basic provincial structure beneath the eyalet. Kaza was a still smaller judicial and administrative district, usually overseen by a judge called a kadi.
The system changed during the 19th-century Tanzimat reforms. From 1867 onward, eyalets were gradually replaced by vilayets, which were more centrally organized provinces. This explains a common quiz mistake: vilayet was the later equivalent of an eyalet, but it was not the name normally used for the empire’s largest administrative units during the eyalet era.