B-Stock is near perfect quality but there will be slight imperfections that do not affect readability at all.
This can include things like ink/overspray residue on cover, binding strings showing in the back of the book, slight imperfections on edges.
 
The SE paperback has:
Colored interior chapter art
Colored map
Colored standard cover inside
SE alternate cover with gold foiling
And sprayed edges on all three sides