Bureaucrats are senior editors. As well as being full Administrators, they have management abilities where they can grant limited user rights. Demotion of Bureaucrats is not done without a community discussion, unless absolutely necessary.
Administrators are trusted editors, equipped with the tools to keep the wiki running smoothly. They can issue blocks to troublesome editors, revert vandalism using the rollback tool, and delete and move pages. They are authorized to use the tools at their disposal to deal with issues facing the wiki to the best of their ability.