reducing router code

1.js

  MyRouter = Backbone.Router.extend({
    routes: {
      "": "mail",
      "inbox": "mail",
      "inbox/categories/:category": "mailCategory",
      "inbox/:id": "mailMessage"
    },

    mail: function(){
      BBCloneMail.MailApp.show();
    },

    mailCategory: function(category){
      BBCloneMail.MailApp.showCategory(category);
    },

    mailMessage: function(messageId){
      BBCloneMail.MailApp.showMessage(messageId);
    }
  });

2.js

  MyRouter = BBCloneMail.AppRouter.extend({
    routes: {
      "": "showInbox",
      "inbox": "showInbox",
      "inbox/categories/:category": "showCategory",
      "inbox/:id": "showMessage"
    }
  });

3.js

new MyRouter({
  app: BBCloneMail.MailApp
});

4.js

  Routing.AppRouter = Backbone.Router.extend({

    constructor: function(options){
      Backbone.Router.prototype.constructor.call(this, options);

      if (this.appRoutes){
        this.processAppRoutes(options.app, this.appRoutes);
      }
    },

    processAppRoutes: function(app, appRoutes){
      var method, methodName;
      var route, routesLength;
      var routes = [];
      var router = this;

      for(route in appRoutes){
        routes.unshift([route, appRoutes[route]]);
      }

      routesLength = routes.length;
      for (var i = 0; i < routesLength; i++){

        route = routes[i][0];
        methodName = routes[i][1];
        method = app[methodName];
        router.route(route, methodName, method);

      }
    }

  });

What are appRoutes, where and how do you define them ?