How do you define the variable type in PHP?

Ans. 

In PHP, a variable does not need to be declared before adding a value to it.

PHP automatically converts the variable to the correct data type, depending on its value.

In a strongly typed programming language, you have to declare (define) the type and name of the variable before using it.

In PHP, the variable is declared automatically when you use it.

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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)