Mama to a Lovie
i don't think there is a difference. but, you don't really need one. i obsessed about finding a black and white one for my daughter's room and spent a ton of money, and you can't even see it!

clavie
I'm not sure, but you can check the size if it's listed. We have a crib skirt (I think! lol) that was part of a bedding set and it only hangs down about 8 inches below the bottom of the mattress so it's nowhere close to touching the floor, even though the mattress is as low as it can go now.

Logan's Mommy
I believe that dust ruffles are for beds and crib skirts are specially made for cribs, so the difference would be size....Unless you found them both under the baby section of the website, in that case they're probably the same.