A bight is a term for a bend, or turn in a line. A bight in a Turks Head refers to the bumps, or turns in the line at the top and bottom of the knot. The leads are the number of round turns the line makes through the knot. A three lead turks head appears to be a three strand braid, except it is tied in a loop with a single line.
The way I count bights is to grab one bight, and start counting the bight right next to that one. When I have gone around the whole knot, I count the one I am holding last. When I count leads, I grab one line from the top of the knot to the bottom of the knot, and count how many lines crosses the one I am holding. Then I count the one I am holding.
If you have a 5 bight x 4 lead Turks Head, and you double the plies, it is still a 5 lead x 4 bight Turks Head. The number of plies is typically not mentioned. Most Turks Heads you will see have two plies. More than two plies will make the knot much more difficult to tighten up evenly.
These rules for counting leads and bights in a Turks Head only apply to common Turks Heads. When you want to try advanced work like Pinapple Knots, or complex Turks Heads, throw the rules out the window because anything goes. When the www.khww.net
website gets back up and running, check out some of the tutorials. I have posted some templates to tie some complex Turks Heads. Most of the templates use a toilet paper tube as a mandrel, and make tying the knot cookbook easy.