Hey, something I know. I feel special!
Anyway, "sipe's" are the thin grooves in the treads of the tire. Which as you have more of them make them better for driving on wet pavement. They kind of act as fingers to grip the surface. As opposed the large grooves which make traction much better in snow, dirt and off-road terrain. So getting them siped means to have more of those thin grooves cut into the treads. If that makes any sense at all?!