A duel layer DVD can basically hold the amount of two DVDs on a single side of one DVD. It solves the problem of having to walk up to the player and "flip" the DVD when the side runs out. Instead of flipping it, you have what is called a "layer change," which is when the DVD switches between the two layers. This results in a slight pause, which depending on how it's done, can either be well hidden or annoying. In Pulp Fiction, for example, the layer change is placed in the middle of Christopher Walken's fantastic monologue.