As a competing highland dancer who wears a kilt I can verify a few things.

A male dancer MUST and ALWAYS will wear black or kilt-toned underwear under their kilt as long as they are competing under SOBHD or SOHDA rules. A female dancer MUST and ALWAYS will wear black or kilt-toned underwear under their kilt as long as they are competing under SOBHD or SOHDA rules. This also is the case for dancers registered with the Academy in NZ and the VSU in Australia.

Nary a kilt pin will be seen on an SOBHD dancer of either sex.

A 'dancer's' kilt is a KILT! The only concession for dancing is a generally lighter weight and the predominance of 'dress' tartans. I don't count the extra buckle as many kilts are made that way.

You see a lot of 4yd, or 6yd 'dancing' kilts being offered at some online kilt shops. This is only because dancers tend to be young and can't use the same amount of fabric. As Barb has mentioned, the amount of fabric in the kilt is directly dependent on the person's width and the sett. A dancer with hips of 28" will not be using the same amount of fabric as a person with hips of 40".

You do see however, the kiltie. A lot of kilt supply business will offer this less expensive option for the young and fast growing dancer. They generally have shallower pleats and less fabric. However, you can never confuse a kiltie with a real kilt.

Our hose must be tartan to match the kilt.

Highland dancers never 'spin'. We turn. However, this year's Seann Truibhas has so many pivot turns we might as well be spinning tops.

BTW, if you're male and want to highland dance, please, please try it out. It's not ballet, it's not jazz. You don't need a partner and it's an awesome workout. It's easy to learn! You don't have to compete to be fulfilled as we have level testing according the the school method used at the studio you learn at.