Declaration: Variables in PHP are declared with a dollar sign ($) followed by the variable name. For example, $name = "John";.

Naming Conventions: Variable names in PHP must start with a letter or an underscore, followed by any combination of letters, numbers, and underscores. They are case-sensitive ($Var and $var are different variables).

Types: PHP is a loosely typed language, so variables can change type as needed. For example, $age = 25; can later become $age = "twenty-five";.

Scope: PHP variables can have different scopes—local (within a function or block), global (throughout the script), or static (preserving values across function calls).

Superglobals: PHP has predefined global arrays like $_GET, $_POST, $_SESSION, and $_COOKIE which are used to handle form data, sessions, and cookies.

$age = 30;       // Integer variable
echo "Name: $name, Age: $age";