We will assume we have a package/project called https://github.com/foo/bar
Most redistributable packages are hosted on a version control website such as Github or Bitbucket. Version control repositories often have a tagging system where we can define stable versions of our application. For example with git we can use the command:
git tag -a 1.0.0 -m 'First version.'
With this we have created version 1.0.0 of our application. This is a stable release which people can depend on. If we wanted to include "foo/bar" then we could create a composer.json and specify the tagged release we wanted: