When a neuron is at rest, it is not sending a signal. The inside of the neuron relative to the outside is negative. There may be attempts to balance out both sides of the membrane, but the cell membrane only allows the passing of some ions.
When a neuron is at rest, potassium ions (K+) have an easy passage through the membrane. It is difficult for Chloride ions (Cl-) and sodium ions (Na+) to cross. The negatively charged protein molecule (A-) is unable to pass through the membrane. Accompanying the selective ion channels is a pump which three sodium ions out of the membrane for every two potassium ions that enter. After all of the forces balance out and the voltage differences between the inside and outside of the neuron have been measured, then the resting potential is achieved.
The resting potential contains information about what occurs in the resting state of a neuron. When a neuron sends information through an axon, then action potential is achieved, which is also known as an impulse or a spike.
A neuron that is at rest show a difference in electrical charges across the membrane. The difference can be measured with the use of small electrodes connected to an oscilloscope or voltmeter.