In PHP, static and self are both keywords used to refer to classes and class members, but they have different meanings and behaviors.

static keyword:

• When used in the context of a class member (property or method), static refers to the class itself rather than an instance of the class.
• A static property or method belongs to the class itself, and it can be accessed without creating an instance of the class.
• Static properties are shared among all instances of the class, and their values are maintained across different instances.
• Static methods can be called directly on the class without instantiating it.
• Example:

class MyClass {
    public static $myStaticProperty = 'Hello';
    
    public static function myStaticMethod() {
        echo self::$myStaticProperty;
    }
}

echo MyClass::$myStaticProperty; // Output: Hello
MyClass::myStaticMethod(); // Output: Hello

self keyword:

• When used in the context of a class, self refers to the class itself and is used to access its own static members (properties and methods).
• self is typically used within the class to refer to its own static members.
• It does not allow for late static binding, meaning it always refers to the class in which it is used, even in the case of inheritance or overridden methods.
• Example:

class MyClass {
    public static $myStaticProperty = 'Hello';
    
    public static function myStaticMethod() {
        echo self::$myStaticProperty;
    }
}

class AnotherClass extends MyClass {
    public static $myStaticProperty = 'World';
}

MyClass::myStaticMethod(); // Output: Hello
AnotherClass::myStaticMethod(); // Output: Hello (not World)

In summary, static is used to define and access static members of a class, while self is used to refer to the current class and access its own static members.