Web Applications
A web application is any application that uses a web browser as a client. The application can be as simple as a message board or a guest sign-in book on a website, or as complex as a word processor or a spreadsheet.
What is a Client?
The 'client' is used in client-server environment to refer to the program the person uses to run the application. A client-server environment is one in which multiple computers share information such as entering information into a database. The 'client' is the application used to enter the information, and the 'server' is the application used to store the information.
Efficacy of User Interface Design
Many technological innovations rely upon User Interface Design to elevate their technical complexity to a usable product. Technology alone may not win user acceptance and subsequent marketability. The User Experience, or how the user experiences the end product, is the key to acceptance. And that is where User Interface Design enters the design process. While product engineers focus on the technology, usability specialists focus on the user interface. For greatest efficiency and cost effectiveness, this working relationship should be maintained from the start of a project to its rollout.
When applied to computer software, User Interface Design is also known as Human-Computer Interaction or HCI. While people often think of Interface Design in terms of computers, it also refers to many products where the user interacts with controls or displays. Military aircraft, vehicles, airports, audio equipment, and computer peripherals, are a few products that extensively apply User Interface Design.

