The current Github install instructions for drush (http://docs.drush.org/en/master/install/#git-clone-ie-manual-install) say as the last step:
From Drush root, run Composer to fetch dependencies.
$ composer install
Since Drupal 7 does not usually have Composer installed, I assume these are Drupal 8 specific instructions.
Where can I find a link to instructions for installing Drush for a Drupal 7 install, where composer is not present?