Bug Testing Marathon (retroactively renamed from Better Than Minecon due to trademark concerns) is a convention held from time to time by various people. Its uniqueness comes from the fact of being a modded Minecraft convention held inside Minecraft itself, letting players meet mod developers while being able to test their mod's features out at the same time.

The name is a play on BetterThanWolves, by the way. Don't read into it too much.