Schultz and chasem explained the term for what is used in kiltmaking.

The reason for steeking in a traditional kilt is because the kiltmaker has to cut out an awful lot of excess material generated by all those pleats; below the hip line all that fabric makes for great "swishing", but above the hip line it causes bulkiness, weight, and insulation.

With the pleat material cut out above the hip line, the pleats below have nothing to "hang from", so the steeking stitches create a hidden, stabilized place for the pleats to hang from in a nice, neat, vertical fashion.

Often, casual kilts with fewer, wider pleats do not have the material cut out. The pleats stabilize themselves from above the hip line and don't need the steeking. (I believe Barb's book says the word, steeking, comes from an older language and means, stitching.)