RubyGems
In plain terms
The package manager and registry for Ruby.
Going deeper
RubyGems distributes Ruby libraries ('gems') and manages their installation and versions. It's the backbone of Ruby's package ecosystem.
Under the hood
Bundler complements it for project-level dependency locking via Gemfile.
Examples
gem install, Gemfile, Bundler, Rails dependencies, ruby libraries.
Think of it like...
Like a marketplace and installer for ready-made Ruby components.