There are many theories regarding the name Kastoria (in Greek: Καστοριά . It has been claimed that the name derives from the Greek word κάστορας/kástoras (beaver), who may have lived in the nearby lake (Lake Orestiada). Other theories propose that the name derives from the Greek word κάστρο/kástro (castle; from the Latin word castrum) or from the mythical hero Κάστωρ/Kástor, who may have been honoured in the area.

The name for the city in Slavic is Kostur/Костур (meaning skeleton, from kost, 'bone'), the Aromanian name is Kastoria and the Turkish name is Kesriye.Kastoria is an important religious centre for the Greek Orthodox Church and is the seat of a metropolitan bishop. It originally had 72 Byzantine and medieval churches, of which 54 have survived. Some of these have been restored and provide a useful insight into Greek Orthodox styles of architecture and fresco painting. The Museum of Byzantine History located on Dexamenis Square houses many examples of Byzantine iconography.