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PHP is dynamically typed — variables don't declare their type:

$count = 5;            // int
$name = "Alice";       // string
$active = true;         // bool
$ratio = 1.5;          // float
$nothing = null;

The type can change at runtime — $count = "hello" is legal. Use gettype($var) or var_dump($var) to inspect at runtime.

PHP has type juggling — automatic conversion in many contexts. "5" + 3 is 8 (string converted to int). "5" . 3 is "53" (int converted to string by the concat operator .). This is convenient until it isn't — modern PHP code uses strict type declarations on functions to prevent surprises.

Constants use define('MAX', 100) or the modern const MAX = 100;. Both are global; constants don't take the $ prefix.