What is the difference between Voltage & Potential Difference ?

voltage is a measurement the same as feet and inches (or metres and centimetres) are measurements.
It is a measurement of electrical pressure, ie Electro motive force,  so 10 volts is a measurement of electromotive force.

Potential difference is the "difference" of voltage between two points.

1) voltage is the difference in potential between the required point (say A) and the infinity(which is taken as reference)
EXAMPLE:  
if i say that at a point A ,the voltage is 5V then it means that the it is at five volt with respect to a infinite point.(whose voltage is taken as 0 volt)
.but potential difference is the difference in potential between 2 points.
EXAMPLE:
if i say the potential difference is  5V it means that its the difference between the 2 points say that it can the difference between two points having voltage 5 and10 or 10 and15 or 15 and 20 etc...

2) the current source is one which will give constant current but infinite voltage but voltage source is one that will give constant voltage but infinite current..
        ^                                                                          ^
        |
      i |
        |--------------------------
        |
        |
        |________________>
               V
the above is current source-you can see that it supplies constant current but any voltage
        |
      V|
        |--------------------------
        |
        |
        |________________>
                 i
the above is voltage source-you can see that it supplies constant voltage but any value of current