Selvedge denim refers to how the denim is produced on the factory. The edges are finished with a special weave (which is usually, but not always, shown on the outseams; that's the double strips you'll see).
Japanese selvedge is made in Japan. Nothing of note beyond that it's a first world country... there are some great Japanese denim factories I'm sure, but you're probably not getting that at the 50-75 dollar range.
Here's a pair that are selvedge, but only have the selvedge seam on half of the outseam. The other half is just sewn up like other non-selvedge jeans (that doesn't mean the denim isn't selvedge though).