Beater

«Beater» is derogatory term used by the players of «Sword Art Online». It is meant to be an insult for beta-testers who play unfairly. It is the result of Kirito trying to protect the dignity of other beta-testers, and make sure that all beta testers (excluding himself), were treated fairly, effectively shouldering the burden of beta testers all across SAO for good.

Beaters are often discriminated and were often treated as unfair players that only care about themselves.

Etymology
«Beater» is a portmanteau of the words «Beta Tester» and «Cheater», the "b" coming from "Beta Tester", and the "-eater" coming from "Cheater". Beta Testers have a bad reputation among the players of «SAO», since most of them had gone solo and did not bother to help the new players after the start of the cursed death game was announced.

The term was created after Kirito defined the difference between the «Newbies», who didn't even know how to level up, and himself. He even refers to the other beta testers as newbies and tells the raid members not to compare them to him, as he got to Floor 10, further than any other beta tester. This way, he chose to create this vulgar term as a way of pushing the discrimination of SAO to a minimum, by driving the hatred onto Beaters. He ended up being the first person to be called «Beater», right after the Floor 1 boss fight. The only known Beater is Kirito; other Beaters most likely hide their status or avoid contact with other players to avoid discrimination.