Knife edging is taking the square edge of the counterweight down to a point in around its rotation. Generally you leave the long edge close to the rod and the chamfered edge to the main journal.
Bull nosing is rounding the front edge of the counterwight so that it cuts through the oil better / easier
X-winging is a slang term from drag racing (not sure if its general) where you cut down the counterweight massively. Imagine its currently almost triangular with one point at the rod journal and the other two at the points of the counterweight. You cut the points off the counterweight making it more diamond shape with a point either end and the wide bit at the crank centre. Does this make sense? Hope so.
All of these mods remove weight from the crank reducing rotating mass and making it spin up faster / rev free-er. It may make idle lumpier and the engine more prone to stalling if done to the extreme with lightened flywheel and pulley etc.