What do you call an operator?

How does the next code run? It's my first time seeing it in C grammar when I think it's going well in GCC ㅜㅜ Where's that thing? What's that called?

#include <stdio.h>
int main()
{
    int x = 10;
    while (x --> 0) // x goes to 0
    {
        printf("%d ", x);
    }
}