What is the ()() operator in C++?

What void operator()() does? Found this while trying to rewrite a C++ program in python but can't even understand the functionality of this method. Its not called from anywhere in code but it is called anyway by a program and cant really understand what is this about? When is something like this called by program itself?

class MoistureSensor {
    const std::chrono::seconds sleepTime;
    std::mutex& mtx;
    std::set<WaterDevice*> devices;

    const int min = 0;
    const int max = 10;
    const int threshold = 3;

public:
    MoistureSensor(const std::chrono::seconds sleepTime, std::mutex& mtx)
        : sleepTime{ sleepTime }
        , mtx{ mtx }
    {
    }

    void subscribe(WaterDevice& device) {
        devices.insert(&device);
    }

    void operator()(){
        for (;;) {
            std::cout << "this\n";
            std::unique_lock<std::mutex> lock(mtx);

            if (isAirTooDry())
                for (auto p : devices)
                    p->sprinkleWater();
            if (isSoilTooDry())
                for (auto p : devices)
                    p->pourWater();

            lock.unlock();
            std::this_thread::sleep_for(sleepTime);
        }
    }
    void foo();
private:
    bool isAirTooDry();
    bool isSoilTooDry();
    int getAirMoisture();
    int getSoilMoisture();
};

Is there an equivalent of something like this in Python?