1. n. 
A coil in an induction logging tool designed to buck out, or reduce, the direct coupling between transmitter and receiver coils. The direct coupling signal is far larger than the formation signal. The bucking coil is wound with the opposite polarity to the main receiver coil, and placed in series with it at a location that minimizes the direct coupling. The combination of transmitter, main receiver and bucking coils is known as a mutually balanced array.