:as in rails routes.rb

The :as option forms a named route.

Usually it’s used in a non-root route. For example:

match '/search' => 'search#search', :as => 'search' # SearchController#search

You could then do something like:

<%= link_to search_path, 'Click Here to Search!' %>

search_path and search_url are defined because of the :as

For a root route, you don’t really need :as because the the URL helpers root_path and root_url are defined for you by Rails.