This article is from the Recreational Figure Skating FAQ, by Karen Bryden with numerous contributions by others.
Most skating blades have the same constant width along its full
length. However, some advanced freestyle figure skating blades have a
concave section ("side honing"). Side honed blades are thicker at the
stanchions and the edge stripe and thinner in between. You can tell
side honed blades because reflections appear inverted.
Another modification to the edge profile found in advanced blades is
"tapering". Tapered blades are thicker at the front near the toepicks
and thinner at the tail, i.e. the edges are not parallel. Parabolic
blades are thinner in the middle section and thicker at both ends.
Some models or custom made blades can be both side-honed and tapered.
These modifications make the blade lighter (because of the removed
steel) and supposedly provide a better grip on the ice. Not
surprisingly, the more laborious manufacturing process translates in a
higher price. Whether they actually provide any real advantage is a
matter of discussion.