Rheobase

In neuroscience, rheobase is the minimal electric current of infinite duration (practically, a few hundred milliseconds) that results in an action potential or the contraction of a muscle.

In the case of a nerve or single muscle cell, rheobase is half the current that needs to be applied for the duration of chronaxie to result in an action potential or muscle twitch. This can be understood better by looking at a strength duration relationship.

This is in short the : "Minimal Electrical current that results in an action potential"

Links
Chronaxie