A meteoroid is a small rocky or metallic body traveling through space. A meteoroid entering the Earth's atmosphere is known as a meteor. If a meteoroid, comet or asteroid actually hits the ground it is known as a meteorite. Meteoroids only range in size from small particles to about 1-meter wide and there is no such thing as a "planet-killer meteor".
Edit:
As the earth still is in one piece, no "planet-killer meteor" has hit it as yet, but if you look here:
en.wikipedia.org/wiki/Vredefort_crater
you will find that the idea of meteorites being no larger than 1 meter (or so) is just ludicrous.
Also if you look here:
en.wikipedia.org/wiki/Chicxulub_impactor
the idea of a meteorite strike causing the kind of destruction that this movie postulates becomes a lot more plausible.