Selvedge is just a way of looping back the warp at the edge of the fabric to produce a self-finished fabric that needs no closing stitch. go look at curtain fabric on the roll in your local John Lewis, that's all selvedge.
Typically it only comes in yarn dyed fabric, not post dyed, as you wouldn't see it. In yarn dyed fabric the lighter coloured/white warp fibre is used to form the selvedge and gives it the characteristic tape edge look and feel.
Don't mistake selvedge for overlocked finished denim, the effect is similar, stiff flat seam, but one will fray the other cannot.
There a little Jap brand that does selvedge on both inseam and outseams, which means they weave the fabric in the shape of the finished garment- that's hardcore, imagine how time consuming that is, they can only make one panel at a time so have to reload the loom four times for each pair of jeans as opposed to rattling off huge long sheets 1 pair of jeans wide.
Selvedge
http://prepidemic.files.wordpress.com/2009/07/selvedge.jpg
fake selvedge
http://i6.ebayimg.com/02/s/000/77/3d/a251_1.JPG
overlocked
http://www.redmonkeyjeans.co.uk/rmc_8.jpg