Butterfly knives are a very specific type of blade that most people don't use on a day-to-day basis. These blades have a handle on both ends so they resemble the wingspan of a butterfly and have become one of the defining symbols in pop culture.
Folding knives, like butterfly knives, are quite popular. Their distinctive opening mechanism is what gives them their name. The handle's pivot point is rotated around each half of the blade as the blade is unfolded.