In a distributed application, it can generally be separated into a client part and server part. When the bulk of the functionality is in the serevr, the client is very 'light' and is refered to as a 'thin client'.
The browser is a reusable thin client. The same client works with millions of web sites and applications. Pretty slick.
We also talk a lot about "zero deployment." If the user has a compatible browser they don't have to install anything else to use an application. This is important when you have public users with many different platforms who shouldn't trust you enough to download a "fat client". It's also important when deploying a fat client to thousands of users in your company is a complex and expensive operation.
A good question is never answered. It is not a bolt to be tightened into place but a seed to be planted and to bear more seed toward the hope of greening the landscape of the idea. John Ciardi