Drop-Off Rate : The rate of change of the inclination in the part of the wellbore where the inclination angle is purposely returned toward the vertical, usually expressed in degrees per 100 feet of course length. (Bul D20)
The Mudblogger (Oilfield, Energy and Related Photographs), Oil Field Glossary, TX, USA 2014. http://mudblogger.com/oilfield-glossary/, (Oil - Amer) {777}