Class extension

Hello all, newcomer to Ruby here and have a quick question a shorthand
version of extend. below is the folder structure I have.

track
|
| - folderA
|
| - temp.rb
|
| - track
|
| - temp.rb

in the temp.rb located in track it’s defined like so

module track

class track < ::track
<snip…>

end

Can someone help me understand this shortcut? Thanks in advance.