What is the difference between require_relative and require in Ruby?

Question

What is the difference between require_relative and require in Ruby?

Answer 1

I want to add that when using Windows you can use require './1.rb' if the script is run local or from a mapped network drive but when run from an UNC \\servername\sharename\folder path you need to use require_relative './1.rb'.

I don't mingle in the discussion which to use for other reasons.