Heroku’s free cloud services begins with the apps – apps which can be deployed to dynos. When you sign up with Heroku, you automatically get a pool of free dyno hours to use for your apps. When your app runs, it consumes dyno hours. When it idles (automatically, after 30 minutes of inactivity), or when you scale it down, your app will stop consuming dyno hours.
You can deploy your free app as many times as you need to, and as long as you have dyno hours, your app will be live and publicly accessible.