I would be reluctant to use the term "DLL" here. It's likely that
gopherq is working in a Linux, UNIX, or BSD environment, and DLL (with rare exceptions) customarily refers to the Microsoft(spit)(R) environment.
The best way to explore the differences between the two is simply to read about each one. Information about the Microsoft(spit)(R) way of doing things is
here.
Pretty complete information about building, maintaining, and using shared libraries in Linux (etc.), including the answer to
gopherq's question, may be found
here.
Hope this helps.