What is a volt?

A volt (V) is just the Standard International unit of measurement for electric potential energy.  It is the force that opposite charges have for doing work if they are pulled apart and then released to fly at each other.  In other words if I pull a charge one direction and the opposite charge the other direction how bad do they want to get back together (like magnets or old relationships)?  This unit of measurement was named in honor of an Italian guy that invented the first battery in 1799, Count Alessandro Guiseppe Antonio Anastasio Volta.  Aren’t you glad they only used his last name?1
 
Digging deeper
Pressure, gravity and elasticity are other examples of potential energy each with their own unit of measurement.  Voltage is a lot like pressure. For example, a unit of measurement of pressure potential is PSI (pounds per square inch).  I put 90 PSI of potential energy into my road bike tires.  If I were to release that 90 PSI of potential energy through the valve stem I could do work like spin a fan, blow up a balloon, or transfer the energy and partially blow up another tire.   Likewise I have 9 volts of potential energy in my 9 volt battery.  If I were to release that 9 volts of stored potential energy I could do work like spin a motor, shock my friend, or transfer the energy and partially charge another battery.   So a volt is just a way to measure potential energy. 
 
So how did they come up with that random unit of measurement?  Way back when one volt was set equal to the potential across a resistance of 1 ohm when a current of one ampere flows through that resistance.  (V=IR)  Or one could also say that it is the potential difference across a wire when a current of one ampere dissipates one watt of power.  There are lots of ways to d efine it all meaning the same thing. 2
 
Volt list
Nerve cell                                                       .070 volts
Batteries (AA, AAA, C, D)                             1.5 volts
Computer USB port                                      5 volts
9 volt battery                                                 9 volts
Car battery                                                     12 volts
Home outlet in North America                   120 volts
Home outlet everywhere else                    230 volts
Business and Industry                                  480 volts
Distribution Lines                                           12,470 volts
Sub-Transmission Lines                                 115,000 and some 57,000 volts
Transmission Lines                                         500,000 and 230,000 volts
Lightning                                                         100,000,000,000 volts

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