Official Definition
Special Publication (NIST SP) – 800-145
NIST https://www.nist.gov/publications/nist-definition-cloud-computing
Cloud computing is a model for enabling ubiquitous, convenient, on-demand network access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction.
In a simple way,
A consumer can unilaterally provision computing capabilities as needed automatically without requiring human interaction with each service provider Capabilities are available over the network and accessed through a standard mechanism Resources are pooled to serve multiple consumers using a multi-tenant model Capabilities can be elastically provisioned and released to scale rapidly outward and inward commensurate with demand Resources can be monitored, controlled & reported providing transparency for both the service provider & consumer of the utilized service
Cloud model
is composed of five essential characteristics
OnDemand Self-Service Broad Network Access Resource Pooling Rapid Elasticity Measured Service
Three Service Models
IaaS PaaS SaaS
Four Deployment Models
Public Private Hybrid Community