Smart client isn't a technology, and it isn't any specific architecture. It is a concept and a style of applications that combines the best of both windows applications and web applications.
They combine the windows applications capabilities of providing rich user experience that are not complex to develop, and that can use local resources which allow it to be responsive, interact with connected devices, and other things that web applications just can't do.
They also combine the best features of web applications which are there ability to be centrally deployed and managed.
Smart client is a pretty broad concept, and it means different things to different people. And it has evolved and been refined, so it's meant slightly different things at different times. However here are the four characteristics that define a Smart Client application:
Offline Capable: Smart clients give users the ability to access critical business information regardless of the availability or quality of a user’s network connection. By caching relevant data locally, smart clients provide users with continuous access to their business information, enabling them to make the right decisions at the right time and in the right place.
Rich User Experience–Smart clients allow people to move beyond viewing static information in a browser. Smart clients provide an interactive and highly responsive user interface, offering users immediate access to critical data. By moving processing and data to the local device or computer, smart clients eliminate the need to contact the server every time a button is clicked. This way, users don’t waste time waiting for screens to refresh or networks to become available.
Central Deployed and Managed: Smart client applications can be centrally deployed and managed, reducing overhead and strain on IT resources. By relying on a local processor, smart client applications can reduce the number of servers required to support an application. Also, bandwidth requirements within the business can be reduced by limiting the transmission between smart client and server to only required data.
Access local resources: Smart clients can make use of local computer resources (such as graphics acceleration cards), attached devices (such as scanners), and local storage. This makes it possible for software developers to create user experiences that are not possible within the Web browser. These new applications enable enterprises to differentiate their software and solutions and to compete more effectively in the marketplace.