namespace

namespace :admin do
  resources :posts
end

↓

admin_posts_path      GET     /admin/posts(.:format)           admin/posts#index
                      POST    /admin/posts(.:format)           admin/posts#create
new_admin_post_path   GET     /admin/posts/new(.:format)       admin/posts#new
edit_admin_post_path  GET     /admin/posts/:id/edit(.:format)  admin/posts#edit
admin_post_path       GET     /admin/posts/:id(.:format)       admin/posts#show
                      PUT     /admin/posts/:id(.:format)       admin/posts#update
                      DELETE  /admin/posts/:id(.:format)       admin/posts#destroy

scope module:

scope module: "admin" do
  resources :posts
end

↓

posts_path      GET     /posts(.:format)           admin/posts#index
                POST    /posts(.:format)           admin/posts#create
new_post_path   GET     /posts/new(.:format)       admin/posts#new
edit_post_path  GET     /posts/:id/edit(.:format)  admin/posts#edit
post_path       GET     /posts/:id(.:format)       admin/posts#show
                PUT     /posts/:id(.:format)       admin/posts#update
                DELETE  /posts/:id(.:format)       admin/posts#destroy

scope

scope "/admin" do
  resources :posts
end

↓

posts_path      GET     /admin/posts(.:format)           posts#index
                POST    /admin/posts(.:format)           posts#create
new_post_path   GET     /admin/posts/new(.:format)       posts#new
edit_post_path  GET     /admin/posts/:id/edit(.:format)  posts#edit
post_path       GET     /admin/posts/:id(.:format)       posts#show
                PUT     /admin/posts/:id(.:format)       posts#update
                DELETE  /admin/posts/:id(.:format)       posts#destroy