The likelihood of a collision is zero, or well below the chance that a random object of the same size will strike the Earth within the next few decades. This designation also applies to any small object that, in the event of a collision, is unlikely to reach the Earth's surface intact. The chance of collision is extremely unlikely, about the same as a random object of the same size striking the Earth within the next few decades. A somewhat close, but not unusual encounter.
Collision is very unlikely.
A close encounter, with a significant threat of a collision capable of causing regional devastation. A close encounter, with a significant threat of a collision capable of causing a global catastrophe. A close encounter, with an extremely significant threat of a collision capable of causing a global catastrophe. A collision capable of causing localized destruction. Such events occur somewhere on Earth between once per 50 years and once per 1000 years.