`System.Net.Http.dll` is a dynamic link library (DLL) that forms part of the Microsoft® .NET Framework, a development platform used to create applications for Windows, web, mobile, and more. The .NET Framework provides developers with a comprehensive set of libraries and tools to simplify and streamline the development process. This particular DLL, `System.Net.Http.dll`, is focused on providing functionalities related to the HTTP protocol, which is foundational for web communication. In essence, it offers classes and methods that enable .NET applications to send and receive HTTP requests and responses. This is critical for any application that interacts with web services, APIs, or needs to fetch data from the internet.

For developers building applications with the .NET Framework, this library abstracts many of the complexities involved with direct HTTP communication. By using the classes and methods provided by `System.Net.Http.dll`, developers can efficiently make web requests, handle responses, and manage errors. If this library is missing or corrupted on a system, applications relying on it might encounter errors or might not function correctly. As a best practice, it's essential to ensure that the correct version of this DLL, and any associated dependencies, are available and correctly referenced in any .NET application that requires web communication capabilities.