1
general::
No difference at all, the same thing, as in She's my sister, or stepsister? same difference. This jocular colloquial phrase dates from about 1940.
American Heritage Idioms
2
general::
Phrase(s): same difference
the same; no difference at all. • Pink, fuchsia, what does it matter? Same difference. • Whether you go or I go, it’s the same difference.
McGrawhill's American Idioms And Phrasal Verbs