At most restaurants, the most briefly-cooked steak you can order is a rare steak, but there's a term for meat that's cooked even less than that: "blue" or "blue rare."
A blue steak's interior is essentially raw, with a just-warmed-through temperature and a slight indigo tint that is natural for uncooked beef that hasn't been exposed to oxygen.
The exterior of the steak is given a nice sear over high heat, but that's it for the cooking step. The finished steak should be very tender, with its truest flavors kept intact.
As long as the meat is of the highest quality, blue steaks are safe to eat because most of the bacteria is present on the exterior. A thorough searing should get rid of it.
Tough or fatty steaks aren't great for cooking to a blue rare, since they need longer cooking times for the fat to render. Leaner options like a tenderloin or flat iron are ideal.