Questions on the use or manipulation of Mathematica variables (i.e. names associated with a changeable value). Use [variable-definitions] or [assignment] for questions on variable context localization, or assignment.
Variable name basics:
Mathematica variables can have multiple letters and numbers in their names, but names are not allowed to begin with a number.
A generally accepted practice is to avoid starting variable names with capital letters, since Mathematica's own built-in commands and variables all begin with capital letters. Using lower-case when creating your own variables helps prevent possible conflicts with built-in commands.
Tips for creative naming (copied from a MathGroup post by David Park):
These are both Symbols and can be used as variables:
LetterSpace has the alias esc ls esc. UnderBracket has the alias esc u[ esc.
Another "special form" that can be used for primed and double primed symbols:
x:02b9 which gives x'
x:02ba which gives x"
These have the Head Symbol and can be used for variables. They are not confused with derivatives and the primes are at the proper level.