The Application layer, one of the five layers in the TCP/IP 5 Layer Model, represents the contents of the data that is sent across the multiple layers.
There are lots of different protocols at this layer, and as you might have guessed from the name, they are application-specific. Protocols used to allow you to browse the web or send receive email are some common ones. The protocols at play in the application layer will be most familiar to you since they are ones you probably interacted with directly before even if you didn’t realize it. You can think of layers like different aspects of a package being delivered. The physical layer is the delivery truck and the roads. The data link layer is how the delivery trucks get from one intersection to the next over and over. The network layer identifies which roads need to be taken to get from address A to address B. The transport layer ensures that the delivery driver knows how to knock on your door to tell you your package has arrived. And the application layer is the contents of the package itself.