How do you call keeping track of instances?

Is there a special term for having a static member keeping track of a class's instances?

From: https://www.oreilly.com/library/view/c-cookbook/0596007612/ch08s05.html

#include <iostream>
#include <list>
#include <algorithm>

using namespace std;

class MyClass {
protected:
   int value_;
public:
   static list<MyClass*> instances_;
   MyClass(int val);
  ~MyClass();
   static void showList();
};

list<MyClass*> MyClass::instances_;

MyClass::MyClass(int val) {
   instances_.push_back(this);
   value_ = val;
}

MyClass::~MyClass() {
   list<MyClass*>::iterator p =
      find(instances_.begin(), instances_.end(), this);
   if (p != instances_.end())
      instances_.erase(p);
}

void MyClass::showList() {
   for (list<MyClass*>::iterator p = instances_.begin();
        p != instances_.end(); ++p)
      cout << (*p)->value_ << endl;
}

int main() {
   MyClass a(1);
   MyClass b(10);
   MyClass c(100);
   MyClass::showList();
}