Cloud computing is the delivery of various services, such as data storage, software, and applications, over the internet without requiring user knowledge of the underlying infrastructure. It provides numerous advantages including data backup, mobility, improved collaboration, low maintenance costs, and data security, while also presenting challenges like internet dependency and vendor lock-in. Different deployment models include public, private, community, and hybrid clouds, and services are categorized into Software as a Service (SaaS), Platform as a Service (PaaS), and Infrastructure as a Service (IaaS).