Remote drush (rdrush) offers drush functionality for drupal websites without SSH access.
Because rdrush doesn't use any actual drush functionality and doesn't need access to the database or code, it can be executed on the client side.
All commands and actions are executed via cURL requests. To make this work, rdrush needs the login credentials of an admin user in the remote drupal environment. It creates a user session and performs all drush-like commands via form requests and submits.