The record identifier encapsulates a number of naming conventions for dealing with records, like Active Records or pretty much any other model type that has an id. These patterns are then used to try elevate the view actions to a higher logical level.

# routes
resources :posts

# view
<%= div_for(post) do %>    <div id="post_45" class="post">
  <%= post.body %>           What a wonderful world!
<% end %>                  </div>

# controller
def update
  post = Post.find(params[:id])
  post.update(params[:post])

  redirect_to(post) # Calls polymorphic_url(post) which in turn calls post_url(post)
end

As the example above shows, you can stop caring to a large extent what the actual id of the post is. You just know that one is being assigned and that the subsequent calls in redirect_to expect that same naming convention and allows you to write less code if you follow it.