Cloud service and deployment models

IaaS rents networks and virtual machines and you run the rest; PaaS runs the platform too (a managed database, an app platform) and you bring code and data; SaaS is the finished application. Public clouds are a provider's, shared; private clouds use the same tools for one organization; hybrid joins the two (by VPN or direct connect); community clouds are shared by organizations with common needs. Elasticity is capacity that follows demand, up and down, by API; scalability is growing to meet it, out (more instances) or up (bigger ones); multitenancy is many customers on the same hardware, kept apart.

See it on real machines