Public simply means that anyone can access the Workiva Community, like they would other sites on the internet. It also means that the site itself (plus any public content within it) will be able to found via an internet search engine, such as Google.

This doesn't mean, however, that the entirety of the site will be completely open for all the world to see, nor will the entire public be able join or interact in the Community. Membership and contributions will still require a Wdesk license. Furthermore, your personal data is not able to be accessed or found via any internet searches, or be seen by any public site visitor. More on info on this can be found here: https://support.workiva.com/hc/en-us/community/posts/360055341632-What-information-about-me-is-viewable-