Public Cloud

A public cloud is one based on the standard cloud computing model, in which a service provider makes resources, such as applications and storage, available to the general public over the Internet. 

Applications, storage, and other resources are made available to the general public by a service provider.
There are limited service providers like Microsoft, Google, etc., who own all infrastructure at their Data Center and the access will be through Internet mode only. No direct connectivity proposed in Public Cloud Architecture.

For public cloud, think a service like Dropbox, which provides file storage to the public, files that can be stored locally but also accessible from the web. 

In terms of public cloud offerings, there are three services:

IaaS (Infrastructure as a Service), PaaS (Platform as a Service) and SaaS (Software as a Service).