Q:

What's the term for "double recursion"?

Here's an obviously recursive function:
function()
{
    function();
}

We would simply call this "recursive"—but what about this (barely) more complex version?
functionLeft()
{
    functionRight();
}

functionRight()
{
    functionLeft();
}

Is there a term for this scenario, e.g., "double recursion"? Or is there no specific term to distinguish this case from the single-function case above?

A:

It's called mutual recursion.

A:

As Jon Purdy said, the example you gave is called "mutual recursion".  The term "double recursion" also exists, but with a different meaning:  for when a function uses two recursive calls.  The classic example is the Fibonacci function"
int Fib(int n)
{
  if (n < 2) return 1;
  return Fib(n-1) + Fib(n-2);
}

The Fib(n) function recursively calls itself twice.

