In this recipe, we will understand application pools. We can simply say that the application pool is the heart of IIS 10.0. Application pools are logical groupings of web applications that will execute in a common process, thereby allowing greater granularity over which programs are clustered together in a single process. For example, if you require every web application to execute in a separate process, you simply go and create an application pool for each application of different framework versions.
Let's say that we have more than one version of a website, one that supports framework 2.0 and another one supporting framework 4.0 or some different application such as PHP or WordPress. All these website process are managed through application pools.