Cloud computing refers to network-based services and resources provided over the internet. It allows users to access computing power, databases, and applications from anywhere without knowledge of the physical location and configuration of the systems that deliver the services. Key characteristics include on-demand self-service, broad network access, resource pooling, rapid elasticity, and measured service. Common cloud services include SaaS, PaaS, IaaS, and cloud storage. Major providers include Amazon Web Services, Microsoft Azure, and Google Cloud Platform.