the differecnce of potentials b/w two points is called the voltage across the two points
it is the voltage which tends the charge or electrons to flow from one point to another eventually producing the CURRENT...
Voltage is an energy given to an electron to move and is created by the accumulation of charges of different polarity, which can be well explained by the Gauss law.
The differecnce of potentials between two points is called the voltage or voltage is the energy per unit charge.
The simple existence of electric charges in different regions and concentrations creates a voltage.
I suppose you mean the simplest form of voltage. Well, The simplest voltage form I know is a static voltage created by charges. It needs no wire, no battery and is sensed to every origin.
1 eV is the energy obtained by an electron through 1 V Potential Difference. Thus, since the charge of an electron is 1.6 x 10 ^ (-19) Coulomb, 1 eV is 1.6 x 10 ^ (-19) Joule.