what is difference between abstract class and abstract function

Question

I know that if I create a abstract class, then I can't create a instance of it, and it will be just a basic class (extending it for other classes). Now I want to know what is abstract function? (or also is there abstract property?)

I saw a function without definition in a abstract class (also the function was abstract), so why? Something like this:

Abstract class test{
      Abstract function index();
}

Answer 1

An abstract class cannot be instantiated. Let's say you have:

Abstract class People {

}

You cannot do $people = new People();

You need to extend it to be able to instantiate it, like:

class Man extends People {

}

$people = new Man();

Regarding Abstract methods, they only contain the method signature in the abstract class and they MUST be implemented in the children classes.

Abstract class People {
  abstract public function getAge();
}
class Man extends People {
  public function getAge() {
    //Blah Blah
  }
}