Utopian Socialism predates Scientific Socialism and is less a concrete idea and more of a misc category. It’s generally categorized as socialistic systems, state acting on behalf of the working etc etc, but without the historical materialistic perspective that Scientific Socialism provides. Utopians might believe that the ruling class can be convinced to give up their power voluntary. They may also believe that Communism is unfeasible or not desirable.

There is a lot of overlap between utopian socialism and modern radlibs and "left" social democrats.