Steak tartare is lean steak (generally bavette or contre-filet) finely chopped with a knife en brunoise (properly, rather than using steak haché). It is mixed with an egg yoke, Dijon mustard, chopped onion, capers, Worcestershire sauce, ketchup, Tabasco sauce, salt and pepper, chopped parsley and olive oil. Many add a raw egg on top.
The name ultimately derives from the ancient Greek Tartarus or hell. When the early medieval Mongolian and Turkic warrior tribes invaded Europe, they were so fierce that it was said they came straight out of Tartarus.
The steppe-raised beef they ate was so tough that the warriors tenderized it under their saddles, then shredded it into bits. In the early Middle Ages this dish arrived in Hamburg, Germany when someone decided to cook it...and the rest is history (although hanburgers may really have derived from fricandelles).
Image by insatiablemunch