Variables are used for storing a values, like text strings, numbers or arrays.
When a variable is declared, it can be used over and over again in our script.
All variables in PHP start with a $ sign symbol.
The correct way of declaring a variable in PHP: $variable_name = value;
Naming rules for variables:-
A variable name must start with a letter or an underscore "_".
A variable name can only contain alpha-numeric characters and underscores
(a-z, A-Z, 0-9, and _ ).
A variable name should not contain spaces. If a variable name is more than
one word, it should be separated with an underscore ($my_string), or with
capitalization ($myString)
