DRUPAL_CACHE_CUSTOM
in includes/common.inc
The block is handling its own caching in its hook_block_view(). From the perspective of the block cache system, this is equivalent to DRUPAL_NO_CACHE. Useful when time based expiration is needed or a site uses a node access which invalidates standard block cache.
<?php
define('DRUPAL_CACHE_CUSTOM', -2);
?>