The stitch is worked by taking the needle/thread across the top of the cloth, but instead of the needle returning below the ground material to the top of the stitch just made, the needle picks up a minute piece of material to one side of this stitch and immediately returns again to the surface of the cloth.
The back of the cloth consequently has two parallel rows of small back stitches outlining the design, rather than that area being covered by thread as with the conventional satin stitch. Stitches produced in this manner tend to be more uneven than satin stitches. It is also regarded by some as a more economic manner of embroidering a design.
Source: THOMAS, Mary (1934). Mary Thomas's Dictionary of Embroidery Stitches, London: Hodder and Stoughton, p. 180.
Digital source of illustration (retrieved 22 February 2017)
GVE