Bukkit is a Minecraft Server mod/wrapper that makes managing and creating servers easier while providing more flexibility with a plugin-based framework. Please note that questions requesting technical support for modded Minecraft crash issues are off-topic.
Bukkit provides a downstream "framework" for developers to build with, making plugins that modify the game in much the same way normal mods do, but with much better backwards compatibility and less compatibility issues.
Please note that questions requesting technical support for modded Minecraft crash issues are off-topic.  This includes crash issues for modpacks and mod loaders. We allow an exception for unmodded or 'Vanilla' Minecraft, please see How do I ask a good Minecraft Bug/Crash Question?
: Arqade Meta: Minecraft crash questions should be made off-topic: yes/no?
: Arqade Meta: What exactly is technical support?