Command
pm-download (alias: dl)

The command “pm-download” or the alias “dl” will download a project. If you are downloading Drupal, it will download to the current directory. If you are downloading a module or theme, it will be placed in the appropriate location.

Syntax
drush dl [project_name-version]

Example
drush dl views or drush dl views-7.x-3.x-dev