Python: What is the `abc.ABC` and `@abstractmethod`?

1from abc import ABC, abstractmethod
2
3class Shape(ABC):
4    @abstractmethod
5    def area(self) -> float:
6        pass
7
8    @abstractmethod
9    def perimeter(self) -> float:
10        pass
11
12    def describe(self) -> str:  # concrete method
13        return f"Area: {self.area():.2f}"
14
15class Circle(Shape):
16    def __init__(self, radius: float):
17        self.radius = radius
18
19    def area(self) -> float:
20        return 3.14159 * self.radius ** 2
21
22    def perimeter(self) -> float:
23        return 2 * 3.14159 * self.radius
24
25# shape = Shape()  # TypeError: Can't instantiate abstract class
26circle = Circle(5)  # OK
27print(circle.describe())  # Area: 78.54