The DLL also called Dynamic Link Library is a file that can be used dynamically by other programs. We create the DLL mainly to hide our confidential code so that we can use the code everywhere but can not see the code. When we talk about the layers or 3 and above tier application we need to understand one thing that why we create layers in our project. We only show some part of code to everyone and hide the main coding part. The benefit is we can use this code but can not see this.