The potential difference between outside and inside of a nerve before excitation is known as
resting potential
When a neuron is not sending a signal, it is "at rest". When a neuron is at rest, the inside of the neuron is negative relative to the outside. The resting membrane potential of a neuron is about -70 mV (mV=millivolt). At rest, there are relatively more sodium ions outside the neuron and more potassium ions inside the neuron.