Asteroid 349507 (2008 QY) is around 1.2 kilometers in diameter, or around 1,000 capybaras – large enough that an impact event (which won't happen now) could be a worldwide catastrophe.
While the asteroid is traveling too far to pose any risk to the Earth, a possible impact event with it could become a worldwide catastrophe.
This is a measurement unit. A bit unconventional, but it's not any worse than using three grains of barley, dry and round, placed end to end lengthwise, or the length of King Henry I's foot.