A skeuomorph is a design feature that's no longer needed but included because previous versions of the item (often made using different materials or in a different way) had whatever it is.
For example the decks of cruise ships are no longer made from planks of wood (as it's a fire risk) but they're likely to be finished in a brown material laid in strips to resemble planks. Modern compact cameras no longer have shutters, but they often make that distinctive cur-lick when a picture is taken, as they have a device added to reproduce it. Chocolates sometimes still come individually wrapped because back in the old days people didn't always eat a whole tinful in one sitting ...
Can you think of any more examples?
Thanks to Julia Hones for telling me about this free to enter competition with a cash prize (there are also paid submission opportunities mentioned on the site)
This opportunity to write for the BBC has been mentioned on several blogs, but here it is again in case you've missed it.
If you'd like my opinions on writing what you know, please take a look here.