Tap pants were originally worn by tap dancers over their panties and hose for modesty when practicing their dance routines. They are similar to shorter half-slips, covering the bottom completely, but with two "legs." The leg openings are not drawn to the skin with elastic, so they look like shorts rather than panties.
Also called cocktail shorts, French knickers, side-cut shorts, and dance shorts, actual vintage pieces are usually much more fluid, like slips, than modern tap pants. But in all cases, they offer much more coverage -- which means more mystery and more silky fabric along your own silky bits).
Tap pants aren't only lovely, they are so comfortable that you'll find yourself making excuses to wear them around the house -- with little else but a bra or cami.
Seeing you with so much more covered than if you'd worn a bare-it-all thong will leave him with a delightful mystery to solve...
Soon he'll be playing detective.
Eventually he'll demand that you spread 'em while he pats you down for additional evidence. I suggest you go ahead and comply -- even if your partner doesn't have the badge, he'll have something else to back up it all up with. *wink*
The vintage black tap pants shown here are from Slip of a Girl's tap pant post; the modern set is from Secrets In Lace.