A Single Page Application is a web application realized with a single page, giving to the end user the experience of a desktop application.
In an SPA, when the user lands inside the application, the HTML, CSS, and JavaScript of the main layout get downloaded; then, with the help of Ajax, the internal view is loaded based on the state of the application and the user actions within the structure of the main layout.
Good SPA uses hash fragment (or the new HTML5 API pushState/replaceState) inside the URL to give the user a way to navigate between pages keeping browser history, using the back and forward button of the browser, and to bookmark the URL to come back later to the current page.
Note
In an SPA, the concept of a page derives from the current status of the system; the user expects that different URLs give different pages, and we normally achieve this with the help of a client routing manager.
Two important points to remember when you realize an SPA are...