There are two versions of the long running stitch: (a) where the stitch is relatively long on the surface of the ground cloth and picks up only a few of the threads of the ground material. The second form (b) consists of a long stitch on the back of the ground cloth, with a small amount of the thread showing on the surface. This version of the long running stitch could be classed as a seed stitch, but the individual stitches of the latter tend to be more closely worked to each other.
Source: THOMAS, Mary (1934). Mary Thomas’s Dictionary of Embroidery Stitches, London: Hodder and Stoughton, p. 177
GVE