A package (also known as a library) contains a set of functionality
that can be invoked by a Ruby program, such as reading and parsing an XML file. We call
these packages 'gems' and RubyGems is a tool to install, create, manage and load these
packages in your Ruby environment. RubyGems is also a client for RubyGems.org, a public
repository of Gems that allows you to publish a Gem that can be shared and used by other
developers. See our guide on publishing a Gem at guides.rubygems.org