Dictatorship is a term that was used widely by the Communist movement (as in the "dictatorship of the bourgeoisie"), and now is used primarily against it (Stalin, Mao, Castro). Laid bare of its connotations, this is what it means to me.
Dictatorship is opposite of consensus. When a group of people do not agree, but need to come to a decision, dictatorships ensue.
Kinds of dictatorships include:
Democracy: The dictatorship of a majority over a minority.
Republic: The dictatorship of a minority over a majority.
Autocracy: The dictatorship of one over all else.
And although dictatorship is the absence of consensus, that doesn't mean people can't consent to being dictated to. Dictatorship does not always involve coercion.