What is a web-based model in which a third-party provider hosts applications that are available to customers over the Internet?

PaaS provides a platform for developers to build and deploy applications, not a hosted application delivered directly to end users.

WaaS (Workspace as a Service) refers specifically to virtual desktop or workspace delivery and is not the standard term for the broad model described in the question.

IaaS provides virtualized infrastructure resources such as VMs and storage over the Internet, not fully hosted applications ready for end-user consumption.

Software as a Service (SaaS) is defined as a distribution model where a vendor hosts applications in the cloud and makes them accessible to customers over the Internet. The provider manages all underlying infrastructure, OS, middleware, and the application itself, while customers simply consume the software through a browser or thin client.