The slip stitch is nearly invisible stitch formed by slipping the thread under the fold of the fabric. It can be used to join two folded edges or one folded edge to a flat side.
An even slip stitch is used to join two folded edges.
Fasten thread to the needle and bring needle and thread out through one folded edge.
Then slip the needle through fold of opposite edge bring the needle out (about half inch) and draw the thread through.
Continue to slip the needle and thread through the opposite folded edges. This is the easy and fast way to stitch a seam. upholstery etc.