What is Ruby's double-colon `::`?

Question

What is this double-colon ::? E.g. Foo::Bar.

I found a definition:

The :: is a unary operator that all

Answer 1

This simple example illustrates it:

MR_COUNT = 0        # constant defined on main Object class
module Foo
  MR_COUNT = 0
  ::MR_COUNT = 1    # set global count to 1
  MR_COUNT = 2      # set local count to 2
end

puts MR_COUNT       # this is the global constant: 1
puts Foo::MR_COUNT  # this is the local constant: 2

Taken from http://www.tutorialspoint.com/ruby/ruby_operators.htm