You're seeing just the macro admin_browser_pipeline, go back to AshAdmin.Router module for more information.
Link to this macro

admin_browser_pipeline(name \\ :browser)

View Source (macro)

Can be used to create a :browser pipeline easily if you don't have one.

By default it is called :browser, but you can rename it by supplying an argument, for example:

defmodule MyAppWeb.Router do
  use Phoenix.Router

  import AshAdmin.Router
  admin_browser_pipeline :something

  scope "/" do

    pipe_through [:something]
    ash_admin "/admin",
      apis: [MyApp.Api1, MyApp.Api2]