What Is a "Hypervelocity" Star

What is a "hypervelocity" star?

A) It is one of the stars in rapid orbital motion close to the supermassive black hole in the galactic center.
B) A star moving faster than the escape speed from the galaxy.
C) This is the name given to a few stars that have been detected moving around the galactic center in the opposite direction from the general galactic rotation. Although their speeds are not unusual, their speeds relative to normal stars are very large.
D) These are stars that move around the galactic center in the middle of the galactic plane, but travel much faster than neighboring stars-seemingly in defiance of Kepler's third law.