Cloud Computing is the on-demand availability of computing power, storage systems, system and application resources such as network, security and others. The following are the nine key components of Cloud Computing.

• Applications
• Data
• Runtime Environment
• Middleware
• O/S
• Virtualization
• Servers
• Storage
• Networking

Cloud Computing again organized in to the following three types of service models.

• SaaS - Software as a Service
• PaaS - Platform as a Service
• IaaS - Infrastructure as a Service

Click Difference between SaaS vs PaaS vs IaaS with examples to know more details.