As far as I understand it, rent seeking means increasing your share of existing wealth without creating any in the process. Raising rent generally on physical properties is one way of doing that, as is mucking about with government to get tax dollars and whatnot coming your way.

As I see it, governments themselves are often rent seeking operations. By increasing taxes, they increase their share of the wealth of the nation, and depending on how that money is used, it could very well be considered rent seeking. Usually the term is used for business sectors interacting with government to get those tax dollars, but I don't think that's the only valid use.