Angle Drop-Off : Rate of change (degrees/100 ft) of the inclination angle in the section of the wellbore that is decreasing toward vertical (refer to "Drop Off"). (Bul D20)
The Mudblogger (Oilfield, Energy and Related Photographs), Oil Field Glossary, TX, USA 2014. http://mudblogger.com/oilfield-glossary/, (Oil - Amer) {777}