The actual word "caviar" was introduced into English in the 16th century. It is believed that it came from French and Italian influence, who inherited the word from the Turkish "havyar". The source of the Turkish "havyar" is apparently an Iranian dialect for the word "egg" in Farcy, "khayah". So to make put it in Kevin Bacon degrees of separation terms:
Iranian (Khayah = "egg" in Farcy) --> Turkish --> French/Italian --> English = Caviar
As to the source, traditionalists define caviar as only the salted roe that is derived from Sturgeon found in the Caspian Sea. Additionally, there only truly existed three types of "caviar", those being Beluga, Ossetra, and Sevruga - As these were the most prominent sturgeon found in the Caspian Sea for centuries.
Modern Day Definition of Caviar:
Today, there are numerous types of "caviar" around the world. Caviar is no longer limited to the Caspian Sea as there are hundreds of farms around the world breading and raising various different types of fish (Sturgeon and Non-Sturgeon) to ultimately produce caviar.
Thus the definition of caviar today has been drastically expanded to include almost all types of salted fish roe, including Sturgeon from all parts of the world, including Salmon, Paddlefish, Whitefish, Lumpfish, and others.
So what does "Caviar" really mean?
Depends on if you are a traditionalist or definitional expansionist. Within the caviar community, the definition is incredibly subjective. Some of our customers define caviar as any processed fish roe (expansionist), while others see it as only those fish roe originating from the Sturgeon Species, including the farmed variety (traditionalist). Still others see caviar as only those eggs processed from the three main Sturgeon (Beluga, Osetra, Sevruga) found in the Caspian Sea (true traditionalist).