What is FaaS, and how does it differ from other cloud models like PaaS and IaaS?

I’ve been hearing a lot about FaaS (Function as a Service) lately, but I’m not entirely clear on how it differs from PaaS or IaaS. From what I understand, FaaS lets you run individual functions in the cloud without managing the underlying infrastructure. How does this model differ in terms of use cases, scalability, and ease of deployment compared to PaaS or IaaS?