I prefer the sub head 'Gathering Stitch' ~ but defer to the general use of Kettle Stitch. Kettle is a bowdlerization of the German word Kettelstitch or Kettel which translates as little chain.
Szirmai calls it the 'Climbing Link Stitch' ~ but this name is rarely used [125205]~1999~p116~Fig 7.16[a]. It is also known as the catch stitch ~ chain stitch ~ catch-up stitch. I am not sure that chain stitch is appropriate, and am uncertain as to where I heard it.
The stitch is used to link the sections of a book together. It is frequently used as the head and tail stitch when otherwise sewing on tapes or cords.
In some ways it is similar to the French Link Stitch [114086].
As the name suggests ~ if it is to gather then two items are involved. The items I refer to are the short stitches that join the sections ~ usually at head or tail. The first of these end stitches is a simple loop that joins the first and second sections. The third section is then gathered tothe first two with the kettle stitch. As always a picture makes this clear....when I get round to it...