A cloud model where computing resources are operated by a third-party provider (Azure, AWS, GCP) and shared among multiple customers over the internet. The customer does not manage the physical infrastructure.
A recurring question in AZ-900 and CLF-C02 asks you to distinguish public cloud from private and hybrid. The key: shared infrastructure, managed by the provider, accessible over the internet.
Public cloud is a concept that can show up on the exam. Check the full guide to see it in context.