Ruby: What does $1 mean?

According to Avdi Grimm from RubyTapas

$1 is a global variable which can be used in later code:

 if "foobar" =~ /foo(.*)/ then 
    puts "The matching word was #{$1}"
 end

Output:

“The matching word was bar”

In short, $1, $2, $… are the global-variables used by some of the ruby library functions specially concerning REGEX to let programmers use the findings in later codes.

See this for such more variables available in Ruby.