Grant is right, as usual.
In regards to formality or "where-can-I-wear-a-certain-style-kilt", the box-pleat is interchangeable with a knife-pleat.
Tartan Hiker did a scientific experiment a couple of winters ago about the heat loss of the two different styles. Search for it and you'll have some very interesting reading.
The pleating options are different with a box-pleat, and I highly recommend the style. I have two of them and really like both of them. I hope you're not thinking that one style is better than the other, 'cause it ain't.