OTP stands for Opposite Track Path. OTP is a variation of a DVD dual-layer disc layout where layer 0 is read from the inside of the disc out, and then switched to layer 1 at the outside of the disc and travels back toward the center. The tracks are written so that the DVD player can rotate the disc in the same direction. This method results in a speedy transition between DVD layers (might be a noticeable but tiny pause during DVD-Video playback).
See also: PTP