Cloud computing refers to the delivery of various computing services, including storage, processing power, databases, networking, analytics, and software, over the internet. Instead of owning and maintaining physical hardware and infrastructure, users can access and utilize these services on a pay-as-you-go basis. Cloud computing provides a flexible and scalable solution, allowing businesses and individuals to scale their resources up or down based on their needs.

Key characteristics of cloud computing includes:

1. On-Demand Self-Service: Users can provision and manage computing resources as needed without requiring human intervention from the service provider.

2. Broad Network Access: Services are accessible over the internet from a variety of devices such as laptops, smartphones, and tablets.

3. Resource Pooling: Computing resources are pooled and shared among multiple users, allowing for efficient utilization and cost optimization.

4. Rapid Elasticity: Resources can be quickly scaled up or down based on demand, providing flexibility and cost savings.

5. Measured Service: Usage of resources is monitored, controlled, and reported, allowing users to pay for only the resources they consume.

Cloud computing is typically categorized into three service models:

1. Infrastructure as a Service (IaaS): Provides virtualized computing resources over the internet. Users can rent virtual machines, storage, and networking components.

2. Platform as a Service (PaaS): Offers a platform that includes tools and services for application development, deployment, and management without the complexity of underlying infrastructure.

3. Software as a Service (SaaS): Delivers software applications over the internet on a subscription basis, eliminating the need for users to install, maintain, and update the software locally.

Additionally, cloud deployment models include:

1. Public Cloud: Services are provided by third-party cloud service providers and are available to the general public. Examples include Amazon Web Services (AWS), Microsoft Azure, and Google Cloud Platform (GCP).

2. Private Cloud: Cloud infrastructure is operated solely for a single organization. It can be managed internally or by a third-party and is dedicated to that organization's needs.

3. Hybrid Cloud: Combines elements of both public and private clouds, allowing data and applications to be shared between them. This provides greater flexibility and optimization of existing infrastructure.

Cloud computing has become a fundamental technology in various industries, enabling cost-effective, scalable, and innovative solutions for businesses and individuals alike.