Identifiers are names given to identify a specific entity (e.g. a variable, function, constant, object, etc), allowing them to be referred to.
Just like algebraic substitutions in maths.
The names can consist of the 26 letters of the Latin alphabet (upper/lower case), the 10 Arabic/Western numerals and the ASCII underscore character _
Start with a number
Be any of the C++ language reserved / key words
ALL identifiers, statements, expressions, etc, are cAse SensITiVe !!!