Loopback links are links that have both ends connected to the same program, much like a FIFO queue. Loopback links are useful as temporary holders of expressions that are being moved between links, or as scratchpads on which expressions can be built up and then transferred to other links in a single call.
Much of the utility of loopback links to users of the C-language MathLink API is obviated by .NET/Link's Expr class, which provides many of the same features in a more accessible way (Expr uses loopback links in its implementation).
Objects of type ILoopbackLink are created by the MathLinkFactory.CreateLoopbackLink method.
ILoopbackLink has no methods; it is simply a type that marks certain links as having special properties.