What does the statement if (counter & (1<<j)) mean and how does it work?

Question

I was working on an algorithm of sub sequences.

What is the meaning of the statement:

if (counter & (1<<j))

within the context of the program below:

void printSubsequences(int arr[], int n)
{
    unsigned int opsize = pow(2, n);

    for (int counter = 1; counter < opsize; counter++)
    {
        for (int j = 0; j < n; j++)
        {
            if (counter & (1<<j))
                cout << arr[j] << " ";
        }
        cout << endl;
    }
}