Imported webservices are the webservices you call (i.e. use) from another system. The result of the call is imported in the Mendix database.
Published webservices are the webservices you publish to other systems. A microflow can be published as webservice. The input paramteres will become the input message of the webservice you publishm, the result type will become the output message. In the published webservice you can check additional associations of the result type to be included in the output message too, i.e. you can define a tree of objects as output/result of your published webservice.