Area on the blade that prevents the sharp edge from contacting the inside of the handle and suffering damage. This is sometimes supplanted by an additional tang pin above the pivots.
Unsharpened spine of the blade that is angled. Some balisongs are also sharpened here or on both sides with either a more traditional look or wavy edges similar to a Kris sword.
Pin meant to hold the blade away from the handle when closed, and a second pin to keep the handles from excessively banging together while the butterfly knife is being manipulated.