A broad category of cloud service models related to cloud computing and remote access, of which the three standard models per NIST are Infrastructure as a Service (IaaS), Platform as a Service (PaaS), and Software as a Service (SaaS). Popular additional services include Backup as a Service (BaaS), Disaster Recovery as a Service (DRaaS), and Desktop as a Service (DaaS or VDI – virtual desktop infrastructure).

With so many different kinds of IT resources and services now delivered as a subscription, XaaS is a somewhat ironic term for the proliferation of cloud services.