I'm not familiar w/DE law so I can't point you to any statute.
If your state has a defining statute, or a definition of "open" or "concealed" you go by that.
If your state does not have such a definition then go by common definition.
Concealed means "hidden from plain sight"
I forget what state defined (or clarified through case law) that open carry means that "the firearm is readily discernable as a firearm to a reasonable person" (paraphrased)
I'm sure someon will have the link handy to that...