However, in electronics, the term "resistance" is routinely applied to the ratio of voltage to current "v/i" at the ports of amplifying devices like transistors, tubes and op-amps, which (as shown below) can become negative.
However, in electronics, the term "resistance" is routinely applied to the static resistance of active devices, which, because they can be negative. For example, the "input resistance", the ratio of voltage to current "v/i" at the ports of amplifying devices like transistors, tubes and op-amps, as shown below can become negative.