Technically the word "régime" refers to any system of control, or more specifically a system of government, but in English language it has become a largely pejorative synonym for "government" or "administration", implying moral disapproval and/or political opposition.

Thus one can speak of "the vicious oppressive régime of Borduria"; but seldom of "the régime in Washington" or of "the current Blair régime".

Compare: Ancien régime, Bush régime, Vichy régime, régime change