This is a name/value collection of IHttpModule instances. It's used by the Modules property of the HttpApplication class to provide a collection of all modules used by your application (as defined in the <httpmodules> section of the application's web.config file).
public sealed class HttpModuleCollection : System.Collections.Specialized.NameObjectCollectionBase { // Public Instance Properties public string[ ] AllKeys{get; } public IHttpModule this[int index]{get; } public IHttpModule this[string name]{get; } // Public Instance Methods public void CopyTo(Array dest, int index); // implements ICollection public IHttpModule Get(int index); public IHttpModule Get(string name); public string GetKey(int index); }