What is factory method?

Factory is a Creational design pattern. Which is used to create different object on condition basis. You can make a method whose return type is an interface/base class and it take a parameter and on the basis of that the method will return object of any class which is implementing that interface. Example:-

    public interface IJunkFood {
        string Prepare();
    }
    public class Burger : IJunkFood
    {
        public string Prepare()
        {
            return "Burger is Ready";
        }
    }
    public class Pizza : IJunkFood
    {
        public string Prepare()
        {
            return "Pizza is Ready";
        }
    }
    public class OtherFood : IJunkFood
    {
        public string Prepare()
        {
            return "Other Junk Food is Ready";
        }
    }
    public IJunkFood GetJunkFood(string type) {
        if (type == "Burger")
            return new Burger();
        if (type == "Pizza")
            return new Pizza();
        else
            return new OtherFood();
    }
    String pizza = GetJunkFood("Pizza").Prepare();
        String burger = GetJunkFood("Burger").Prepare();