1. A difference in the arrival time of two events. 2. A delay in the arrival time. Lagging refraction or reflection arrivals may indicate subsurface structure or delay caused by weathering variations, phase shifts in filtering, shothole fatigue, etc. Negative of lead. 3. The phase angle by which the current is behind the emf in an inductive circuit. 4. The time delay between the breaking of the bridgewire in a detonating cap and the resulting explosion. 5. To be behind. 6. The distance a sensor is behind the point where location is determined, as the distance an aerosurvey bird is behind the aircraft or a fish behind a boat; also called layback. 7. The time for cuttings to travel from the bottom of a drill hole to the surface.