Sure, Dennis. Here's one:
Put simply, a plumbing manifold is a device used to create multiple outputs of equal flow emanating from a single (or as pictured, two or three) input, or source tubes. Of course the one pictured is not being used in an aquarium, but it's a good enough picture for getting the point across. The manifolds used in aquaria are often of PVC construction, but not always.
This one pictured is taking the input (vertical tubes, top center), and plumbing them out to multiple taps (the side mounted, horizontal tubes) going to various locations in a house. I've seen ones on DIY home shows that have the inputs coming from either side, plumbed horizontally, and the outputs centered between these inputs; shooting off vertically. In this way, all the outputs are guaranteed equal strength. The one I remember was sending hot water to all points in a large house. With such a manifold, if the dishwasher was running in the kitchen, a person showering didn't lose hot water momentarily when the dishwasher kicked in.
manifold plumbing questions 
