Cloud computing allows users to access computing resources over the internet. It provides several advantages like cost reduction, increased storage, and mobility. However, security, data privacy, and reliability of service are limitations. There are four cloud models - private, community, public, and hybrid clouds. The three main types of cloud services are Software as a Service (SaaS), Platform as a Service (PaaS), and Infrastructure as a Service (IaaS). SaaS provides software access over the internet, PaaS provides platforms for application development, and IaaS provides virtual computing infrastructure and resources.