What is cloud computing, and what are the differences between public, private and hybrid cloud?

Cloud computing delivers computing resources on demand over the internet, paid for by consumption rather than purchased outright. The shift is from capital expenditure on hardware you must size for peak demand, to operating expenditure that scales with actual use.

The service models:

• IaaS — virtual machines, storage, and networking. You manage the operating system upwards. AWS EC2, Azure Virtual Machines.
• PaaS — the provider manages the OS and runtime; you deploy applications. Azure App Service, AWS Elastic Beanstalk.
• SaaS — a finished application. Microsoft 365, Salesforce.

The deployment models:

• Public cloud — shared infrastructure from a provider. Lowest cost, effectively unlimited scale, no hardware to manage. The trade-offs are less control and dependence on the provider.
• Private cloud — dedicated infrastructure, on-premises or hosted. Chosen for regulatory requirements, data residency, or specific performance needs. More control, higher cost, and you still manage the hardware.
• Hybrid cloud — both, connected. The most common reality: legacy or regulated workloads stay on-premises while new work goes to public cloud. Also used for burst capacity and disaster recovery.
• Multi-cloud — more than one public provider, for resilience, negotiating position, or because different providers suit different workloads.

Note: Two practical points worth raising: cloud is not automatically cheaper, and cost control requires active management; and the shared responsibility model means securing your data and configuration remains yours regardless of provider.