What is ltng:allowGuestAccess?

Hello ,

Its a Interface,This interface lets you build your app with Lightning components, and deploy it anywhere and to anyone.

A Lightning Out dependency app with the ltng:allowGuestAccess interface can be used with Lightning Components for Visualforce and with Lightning Out.

Using Lightning Components for Visualforce, you can add your Lightning app to a Visualforce page, and then use that page in Salesforce Tabs + Visualforce communities. Then you can allow public access to that page.
Using Lightning Out, you can deploy your Lightning app anywhere Lightning Out is supported—which is almost anywhere!