Tableau Public is a piece of software, similar to Tableau Desktop, that you can download and use for free with some limitations: you need to publish your work online in a public environment, and you don't have access to all the connectors that are available in Tableau Desktop.
Tableau Public is, in fact, much more than that.
On the Tableau Public website, you can find a Viz Of The Day section on the home page (every day, a new Workbook is promoted by Tableau: https://public.tableau.com/en-us/s/), and many featured visualizations in different categories (Greatest Hits, Sports, Social Goof, and so on). You can find a list of the current featured authors, a blog, and many resources to keep learning. You can also search...