Rerolling originally means to stop playing the class you play and play a different class including leveling, gearing and all that. VG just corrupted the term rerolling and altered its' meaning.
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Pretty much this.
In a Role Playing Game, short RPG, which can be a computer game including an MMORPG or pen and paper.
1. To abandon a character and create a new one
2. To abandon a character and create a new one of a certain character class.
1. "If you're playing a paladin, just reroll."
2. "They nerfed my druid, I'm gonna reroll hunter."
This its what basically Re-rolling means and yeah many people got the meaning of the word in a bad way when you could make ur warrior into X class here etc.