Difference between a "dancing" kilt and any other, and liners?

[The Wizard of BC]

To expand the explanation of the liner of a Kilt a little further.

Inside a Traditional Style Kilt in the area of the Fell which is where the pleats are sewn down and tapered, there are added internal constructions. Most noteabley are the Stabilizer which spans across the back from one buckle to the other to take the stresses of wearing the Kilt and keep them off the stitching. And the interfacing which is a piece of "Hair Canvas". This is not normal canvas but a product with is very loosly woven and stiffer in the vertical direction than in the horizontal. This interfacing reaches the entire length of the Kilt from one apron edge strap all the way across to the other apron strap.
The purpose of the Stabilizer and Interfacing is to take the stresses of wearing and moving in the Kilt and to help the Kilt keep its shape without puckers and popped stitches.
The excess fabric inside the pleats are also cut-away to thin the back of the Kilt preventing "Pillow butt"

The Liner is then sewn in to cover all the internal construction details.

Some think that the liner is there to keep the Kilt clean. Well, if that were the case then it would be removable and washable.

No, it's there simply to cover up all the unseen stuff built into the Kilt.

[The Wizard of BC]

To quote from "The Art of Kiltmaking"

"There's no such thing as a 'dancer's kilt', and kilts for dance competitions are measured and laid out exactly the same way as a kilt for a man."

pg. 25 second printing.