Most commonly an athletic shoe that has been dressed up enough to pass for formal wear. Common examples are Air Jordan's in a full black color scheme with touches of white often in the sole. At first glance they appear formal enough, upon later examination you're just a kid in a grown up body in fancy tennis shoes.
"Honey, can I wear my tuxedo shoes or do I have to find where my Doc Martin's are stored for the wedding you're making me go to?"
"You want to wear your Jordan's again?"
"Yes."