I believe it’s specified by REST. Here’s a list for ya:
GET /items #=> index
GET /items/1 #=> show
GET /items/new #=> new
GET /items/1/edit #=> edit
PUT /items/1 #=> update
POST /items #=> create
DELETE /items/1 #=> destroy
Edited to add to get all those routes, in config/routes.rb, simply add map.resources :items