Games : What is a "Power Throw," and who all gets one?

I remember while watching some Super Smash Bros Brawl Tournaments, the commentators were talking about how one of the players (Ness) went for a "Power Throw (his back throw)." But, what defines a "Power Throw" from a regular throw, and who all gets one?

This question applies to all SSB games that have "Power Throws."