Absolutist forms of government (in those days generally the absolute monarchy form) is a form of government in which the monarch exercises ultimate governing authority as head of state and head of government. That is to say, he/she is in no way restricted or limited by any constitution or law.
This enabled the Monarchies of Austria, Prussia and Russia to do what they liked, and in general this meant imperialist politics. A good example is what the three of them decided at the Congress of Vienna: they just divided Poland and each one of them took his piece of the territorial pie.
