Gobelin Stitch is the family name for needlepoint stitches which are longer than one thread and are not part of Cross or Box Stitches. They can be upright, Straight Gobelin, slanted on the true diagonal, Diagonal Gobelin, or, slanted along another diagonal, making an oblique stitch.
Straight Gobelin can be any length you like as long as it crosses at least two canvas threads and is made in a straight line. Stitches crossing only one thread are not stable on needlepoint canvas and should be avoided.
A fun way to use this stitch in a border is to make a stitch called Beaty. In it pairs of stitches alternate between two different lengths. They are faced with another set of stitches which are a mirror image. You can also make this stitch in two different threads, alternating by pairs of Gobelin Stitches or by rows.