What are self and static in PHP and how are they used?

Self refers to the current class where the code is defined. Static refers to the class that was actually called at runtime.

<?php

class MyClass {
    public static function myStaticMethod() {
        // Here self:: refers to MyClass
        echo self::class . "::myStaticMethod() called\n";
    }

    public static function delegatedStaticMethod() {
        // Here static:: refers to MyClass or the child class that called the method
        echo static::class . "::delegatedStaticMethod() called\n";
        self::myStaticMethod(); // Calls method from MyClass
    }
}

class MyChildClass extends MyClass {
    public static function anotherStaticMethod() {
        // Here static:: refers to MyChildClass
        echo static::class . "::anotherStaticMethod() called\n";
        self::myStaticMethod(); // Still calls method from MyClass
    }
}

MyClass::myStaticMethod(); // MyClass::myStaticMethod() called
MyClass::delegatedStaticMethod(); // MyClass::delegatedStaticMethod() called, MyClass::myStaticMethod() called
MyChildClass::delegatedStaticMethod(); // MyChildClass::delegatedStaticMethod() called, MyClass::myStaticMethod() called
MyChildClass::anotherStaticMethod(); // MyChildClass::anotherStaticMethod() called, MyClass::myStaticMethod() called

?>

Keyword	Binding	Used for
self	Binding at compile time to the current class	Access to static properties, constants, and methods of the current class.
static	Late static binding to the class that called the method	Access to static properties, constants, and methods in the context of the calling class (can be a child).

The main difference is late static binding (static), which allows inheritance to override static behavior, whereas self always refers to the class where the code was defined.