A White Screen of Death means when you access your website, you see nothing but a blank page. There can be multiple reasons behind a WSOD, the most common ones being compatibility issues with a module or a theme. Of course, the “incompatibility” itself can have multiple faces: a plugin may have a conflict with another plugin, or a plugin may not be compatible with the latest version of Drupal. Similarly, a theme may also experience compatibility issues with Drupal after an update. The easiest solution is to retry and revert to a backup or rename your /sites/all/modules folder.