Three healthcare firms jointly own and share the same cloud resources to meet their computing needs. Which cloud model does this represent?

In this particular example, these three healthcare companies using a public cloud because the companies share the resources.

They are using the model IaaS (Infrastructure as a service) this mean an external company is sharing their resources to this three companies, they can store data in this model, Infrastructure as a service gives you the highest level of flexibility and management control around your IT resources, is the best benefit in this model, you buy only what you need.