Why would any sane human being laugh at that? We all had to start somewhere.
A sump, in aquarium terms, is basically a second tank placed under (or in extreme cases, above) the main tank. The are often used for filtration, growing things, bases for overflow filters, ect. A sump can be used for one thing, or it can have many purposes. They are a good place to isolate the small bad guys that show up in reef tanks, ie. whelks, pyramid snails, pea crabs, ect.
They are a good investment, but are occasionally impossible to use with some setups, such as one with a tube stand.
-Lynden