Framework application is the kind of generic application and it can be extendable across the organisation or any industry. Let's say pega has released few of the frameworks like customer service, smart investigate and so on. The client who is interested to use the customer service can get it from pega and built an implementation application on top of it.
In a nutshell, framework provide the specific functionality where client can plug it and use that. It reduces the effort of creating the whole functionality from scratch.
Implementation application generally used to create either the application from scratch or you can built an application on top of framework applications.
Note: From 7.4 or 7.2, pega introduces the multiple built on applications concept. Prior to these versions, we need to create a framework application where we can keep all the reusable components in it and create an implementation on top of it.
But now, we can create an implementation application with multiple built on applications. Please go through the below video to know more about multiple built on applications
Let's say in our case, we are using the Pega Customer Service framework which was provided by pega. This is a kind of call centre application which is used to resolve customer issues. If I want to develop this application in pega, it would definitely take some time as it is a big application which supports multiple channels (call, chat, email).
To avoid all this work from scratch, I can directly get the framework application from pega and built my implementation application on top of it. In this way, the overall development effort would be reduced and In a short time with the little customizations in the implementation application, I can go to production.