Routing frameworks for SPAs update the browser’s URL as the user navigates through the app. Conversely, this allows changes to the browser’s URL to drive navigation through the app, thus allowing the user to create a bookmark to a location deep within the SPA.
UI-Router applications are modeled as a hierarchical tree of states. UI-Router provides a state machine to manage the transitions between those application states in a transaction-like manner.
Taken from the UI-Router Github page