What is "mapserver"

MapServer is an open source development environment for building spatially enabled internet applications. It can run as a CGI program or via MapScript which supports several programming languages (using SWIG). MapServer was developed by the University of Minnesota — so, it is often and more specifically referred as "UMN MapServer", to distinguish it from commercial "map server". MapServer was originally developed with support from NASA, which needed a way to make its satellite imagery available to the public.