What is “<Cycle 1>” an indication of in Xdebug?

Question

I have an xdebug profile on a php script that I parsed with kcachegrind. Here is a screenshot showing that the most time spent inside any given function was spent inside <cycle 1> and the top 'Callers' were made from 'include' and 'include_once' in index.php.

This profile was run during a stress-test using apache 'ab' so there were many concurrent connections occurring.

What does <cycle 1> indicate on an xdebug profile?