You can find "definition of the skate blade" in ISU rules here
My understanding is that it goes back to the "compulsory figure times". I was told that at one point some skaters "tried" to compete (only in compulsory figures) using different blade profile. It was similar to overturned trapezoid.Code:Rule 500 Definition of the skate blade and clothing 1. Figure Skating blades used during competitions must be sharpened to produce a flat to concave cross section without change to the width of the blade as measured between the two edges. However, a slight tapering or narrowing of the cross section of the blade is permitted
The advantage of this blade profile was to avoid "flats" or "double tracings". The ISU reponse was the "Definition of the skate blade".
I'm just curious if someone knows who were the skaters (or coaches) who "invented" this blade and when it happened.