final class PW_User_Geo {

• Declares a class named PW_User_Geo.
• The keyword final means this class cannot be extended — no other class can inherit from it.
  • 🔒 This is often used in WordPress plugins to prevent developers from accidentally overriding core functionality.

const TRANSIENT_PREFIX = 'pw_user_geo_';
const VERSION          = '1.1.1';

• These are class constants (like variables that can’t change).
• TRANSIENT_PREFIX → used as a prefix when saving data to WordPress transients (temporary cache stored in the database).
• Example: 'pw_user_geo_' . md5($ip) creates a unique key for caching each IP’s location lookup.
• VERSION → keeps track of the plugin’s version, useful for debugging, migrations, or cache busting.

private static $instance = null;

• This creates a static property to hold the single instance of this class.
• Used for the Singleton pattern (only one copy of the class exists).

public static function instance() {
	if ( null === self::$instance ) self::$instance = new self();
	return self::$instance;
}

• This method ensures that:
  • If no instance of PW_User_Geo exists yet (self::$instance is null), it creates one (new self()).
  • Returns the existing instance.
• So every time you call PW_User_Geo::instance(), you get the same object, not a new one.