No difference in voltage between input 1 and input 2 describes what condition?

The term "equipotential" refers to a condition where no difference in voltage exists between two points, in this case, input 1 and input 2. In an equipotential scenario, the electrical potential at both inputs is identical, indicating that the two points are at the same voltage level. This concept is essential in understanding how electrical signals and potentials behave in electroencephalography (EEG) and other electrophysiological measurements, as it informs you that there is little to no electrical activity or differential potential across these input points.

In contrast, biopotential refers to the electrical potential generated by living cells, such as neurons or muscle fibers, typically in relation to their activity levels. Quadripotential and tripotential terms are not commonly used in a standard context and lack a straightforward definition related to EEG practices. Hence, choosing equipotential accurately describes the situation where there is no voltage difference between the specified inputs.