Subrouting is the idea of dividing an application's router into a number of module-specific routers. In a small- or medium-level application, you may never need something like this. However, for an application with multiple modules, a single router that handles all of the routes soon turns into a huge, unmanageable class. So, it is always preferable to split the main router into a set of module-specific routers.
Backbone.Subroute (https://github.com/ModelN/backbone.subroute), a wonderful extension developed by Dave Cadwallader, provides the functionality that we are talking about. It lets the base router delegate all of the module-specific routes to the subrouter associated with that module. Let's understand the difference between a router and subrouter with the two examples that follow.