Beginner at programming. C++ colon on line 9 included in this example code from textbook. I understand up to line 8 but what does the colon do?

Colon on line 9 is throwing me off. I'm not sure what its purpose is.

    #include <iostream>
    using namespace std;

    const int TOTALYEARS = 100;

    int main()
    {
        int ageFrequency[TOTALYEARS]; // reserves memory for 100 ints
        :
        return 0;
    }