Linux is a operating system based on the UNIX operating system developed by Bell Labs (AT&T) in the 1960's. It is faster at file operations and more secure than Microsoft Windows but requires more customization than Microsoft Windows. Most software for Linux in Open Source and available for free. Most web servers that host more than one site run a version of Linux annd the protocols for web traffic are based on the original Unix communication standards.
There are many different versions (referred to as distributions) of Linux available but the most popular for Personal desktop or Laprtop use are Ubunto and Fedora. For server there is the top of the line RED HAT Linux, CentOS, SUSE and several others.
To answer your question I would have to say a Linux box is a server that requires very little maintenance when properly configured. The company I work for has 2 Linux techs that are primarly available for configuration questions and building new servers. Compare this to the 8 Windows techs and 6 Exchange techs that are always trying to fix some bug or problem with Microsoft Products.