A cheap knock-off of a name brand item, usually an item of poor quality. Though Wal-Mart is usually the origin of said item, a Wal-Mart special can come from any store.
1.) Jimmy wanted an iPod for Christmas, but his mom got him the Wal-Mart Special and it's already broke!
2.) Patrick: "Hey guys, check out the new rims on my car!"
Michael: "Wow, are those made of plastic? You must have cheaped out and got the Wal-Mart Special!"