With the stem stitch, the thread travels forward, normally from left to right, on the surface of the cloth, before it enters the ground and travels back for a short distance, and then emerges again on the surface of the ground cloth, travelling forwards again, following the desired line of the design. The thread should always be kept below or to the right of the needle. The stem stitch resembles the outline stitch, the difference being the direction in which the stitches overlap: the stem stitch overlaps in a Z-direction, while the outline stitch overlaps in an S-direction.
The stem stitch is also known as the crewel stitch, stalk stitch and South Kensington stitch.
Source: THOMAS, Mary (1934). Mary Thomas's Dictionary of Embroidery Stitches, London: Hodder and Stoughton, pp. 189-190.
Digital source of illustration (retrieved 30 May 2016)