The Free Beacon  illustrated it perfectly:
Hillary Clinton’s chief of staff worked as an unpaid “advisor” during her first four months at the Department of State while holding outside positions with New York University and the Clinton Foundation, department officials told the Washington Free Beacon.
The State Department initially said in June that Mills was appointed as a “Special Government Employee” from January until May of 2009, a designation that allowed her to avoid certain ethics rules and hold outside employment.
However, last week the department said that after further investigation it had found that Mills was not technically designated a special employee in 2009. Instead, she had been appointed an unpaid “expert/consultant” for her first four months with Clinton, according to officials.