Craftsy.com provides instructions on how to sew a slip stitch. Both knitting and crocheting use the term "slip stitch." LionBrand.com offers instructions on knit and crochet slip stitch techniques.
In sewing, the slip stitch refers to a type of hand-sewing that is commonly used to finish hems. After the desired hem is folded into place, it is secured by sewing through the edge of the folded hem and small bits of threads on the outside fabric. Even and properly placed stitches produce an almost invisible seam with the thread hidden between the folds of the hem. Couture sewing often employs the slip stitch technique.
Knitters use the slip stitch to create textured patterns, mosaic knitting, and double knitting. It is often abbreviated in knitting patterns as "sl." Knitters work a slip stitch by moving a stitch from one needle to the other without actually working it.
In crochet, the abbreviation "sl st" refers to the slip stitch. Rather than a method of producing fabric, most crocheters consider the slip stitch a utility stitch. It is an effective method of moving the yarn to another part of a row, joining stitches or seaming. The slip stitch is a relatively flat stitch that adds only a small bit of height to the finished work.