Web services are Web apps by definition and many, although not all, websites contain Web apps.
A Web application (Web app) is an application program that is stored on a remote server and delivered over the Internet through a browser interface.
Within the mobile computing sector, Web apps are sometimes contrasted with native apps, which are applications that are developed specifically for a particular platform or device and installed on that device. However, the two are not mutually exclusive because many applications contain elements of both native and Web apps. Programs that combine the two approaches are sometimes referred to as hybrid applications.
From a technical view-point, the web is a highly programmable environment that allows mass customization through the immediate deployment of a large and diverse range of applications, to millions of global users. Two important components of a modern website are flexible web browsers and web applications; both available to all and sundry at no expense.
Web browsers are software applications that allow users to retrieve data and interact with content located on web pages within a website.
How do web applications work?
The figure below details the three-layered web application model. The first layer is normally a web browser or the user interface; the second layer is the dynamic content generation technology tool such as Java servlets (JSP) or Active Server Pages (ASP), and the third layer is the database containing content (e.g., news) and customer data (e.g., usernames and passwords, social security numbers and credit card details).
The figure below shows how the initial request is triggered by the user through the browser over the Internet to the web application server. The web application accesses the databases servers to perform the requested task updating and retrieving the information lying within the database. The web application then presents the information to the user through the browser.