In embroidery stem stitch is used to create lines and curves, as opposed to blocks of colour. It is a popular stitch for outlining either hollow pictures or pictures which are infilled by another stitch.
Stem stitch can often be distinguished from split stitch by a slight spiralling effect along the line of thread which causes it to glisten less than split stitch. It also often stands a little higher (further out from the fabric) than split stitch, making it stand out a little better.
- How to do Stem Stitch - http://www.embroiderersguild.org.uk/stitch/stitches/stem.html