There are different Usages of the letter V.
1. the twenty-second letter of the English alphabet
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
This letter denotes the next after T in a set of items, categories, sizes, etc. e.g. It also denotes the twenty-second of twenty two or more hypothetical people or things.
v = velocity, V = Volume and V = five as in Roman Numeral. Besides, V letter of the English Alphabet is used in Vatican City as the International Vehicle Registration.
In Chemistry V = Vanadium the 23rd element of the periodic table and in Physics V = Voltage or Potential Difference as in V = IR where V is the electromotive force that would carry one ampere of current = I, against one ohm resistance = R.
The most Common Noun which is used to learn this letter at the Nursery level is V; V for Van.