Does drush have built-in variables or macros? Does drush have built-in or predefined variables or macros?

An example would be like the base directory of the Drupal installation, database name, passwords etc? Something like the values displayed in drush status
If you source the file examples/example.bashrc from your ~/.bashrc file, then you can do useful things like cd %root or cd @site:%root.  Without sourcing that file, you can use cd $(drush dd %root).  If you want to go to a module or theme directory, cd $(drush dd %devel) also works.  Using the %path aliases without qualifying them with a @site alias does, of course, require that your cwd be inside some Drupal site (or $options['root'] must be set in some drushrc.php file).