What's The Difference Meaning

(idiomatic) The difference doesn't matter; so what.

Example: How are they different
1908, Lucy Maud Montgomery, Anne of Green Gables Chapter XII
  "I don't see why it's any more ridiculous to wear flowers on your hat than on your dress," protested Anne. "Lots of little girls there had bouquets pinned on their dresses. What's the difference?"
1997, Ed Bott, Using Windows
  What's the difference between new Windows programs and old ones? If you're paying close attention, you'll notice subtle differences in the way new 32-bit Windows programs look. Dialog boxes, for example, are likely to have tabbed pages ...
2010, Patricia O'Grady, Tales of the Whosawhachits: Key Holder of the Realms:Book 1
  â€œGenies, fairies, whatever, what's the difference, bring them here I want to talk to them,”