The Seed Stitch is a running stitch. It is exactly the reverse of single darning in that it is a short stitch on the upper side and a long stitch underneath. It may be used as a filling stitch, and is often used in lettering in connection with heavier works.
The above definition does not give an embroiderer who may be new to this stitch much information about it. Questions such as what applications would benefit from using it or what variations of this stitch exist? Below is, I believe, a clearer explanation of what the stitch is and its many uses.
This stitch is a small straight stitch and is quite versatile. See illustration below. It can be used as light or dense filling depending on how many stitches you make and how closely you make them to each other. The stitches can be worked in a uniform manner or randomly. They can be stitched as single or they can be doubled so that two stitches lay side by side. Whichever way they are used, they will add texture to the embroidery piece.
This stitch can, of course add color to an embroidered piece, such as using this stitch to make black "seeds" on a strawberry. If used creatively, shading can be produced by making the darker areas dense with seed stitches and stitching fewer as lighter areas are needed.
More samples of this stitch will be added in the future so that you may see its true versatility.