OTP stands for One-Time Pad, which is actually a bit of an odd thing since the definition rather closer fits XOR pads than what the OTP actually is. The OTP is a 256-byte unique value from which several important keys are derived. Admittingly, it's too big to be outright considered a "key" in its own right since most keys are 16-byte(128bit) or 32-byte(256bit) long and the OTP is much larger. I believe -how- the keys are derived is yet unknown but then the OTP can still be used to encrypt or decrypt stuff in a valid fashion.