User blog comment:Poseidon133/What is the Difference between Admin and Bearucrat/@comment-5558012-20130817024404

To clarify everything here, these are the important  differences between the two groups:

An Admin can (a Bureaucrat cannot):
 * Delete/undelete pages
 * Protect/unprotect pages
 * Edit Theme Designer & Mediawiki pages
 * Grant/Remove Chat Mod. Rights and add Bot group
 * Act as a Chat Mod.

A Bureaucrat can (an Admin cannot):
 * Grant/Remove Rollback and Admin rights
 * Grant Bureaucrat rights

Both groups can:
 * Block/unblock users
 * Remove Bot group

There are other smaller privileges they have in common, but many of the smaller tools that Admins have Bureaucrats don't.

Refs: Help:User access levels and Special:ListGroupRights.