What does impartial advice mean?

It is almost an erroneous combo of Words because advice is usually an opinion and impartial meaning your feelings or prior ideas to the situation should not sway your response.

However, if you are not trying to be sematic about it, splitting hairs if you like then:

I would propose that impartil advice would be described as the opinion you give someone that is not biased by any personal feelings on the matter. Such as a Judge might give or someone who was trying to be objective, just using facts no opinions/feelings.