According to "The NIST Definition of Cloud Computing," in IaaS, "the capability provided to the consumer is to provision processing, storage, networks, and other fundamental computing resources where the consumer is able to deploy and run arbitrary software, which can include OSs and applications. The consumer does not manage or control the underlying cloud infrastructure but has control over OSs, storage, and deployed applications; and possibly limited control of select networking components (e.g, host firewalls)."

Virtualization isn't merely a tool for creating virtual machines-it's the core technology for enabling cloud computing. We use virtualization all throughout computing, from full operating virtual machines to virtual execution environments like the Java Virtual Machine, as well as in storage, networking, and beyond.
Reference: CSA Security Guidelines V.4(reproduced here for the educational purpose)

The four cloud deployment models are
1. Public
2. Private
3. Hybrid
4. Community

IS0 27017 provides Code of practice for information security controls based on ISO/IEC27002 for cloud services.