Before delving into the definition of Cloud Computing, we'll go over a few foundational concepts at a high level.

What is On-Premise:

When physical hardware and software are hosted and directly managed inside a business's physical location, we call it as On-Premise.

What is Off-Premise:

When physical hardware and software are tied to a particular location (not inside a business's physical location), often leased space - we call it as Off-Premise.

What is Cloud?

“Cloud” in IT refers to: A massively interconnected network of servers meant to provide computer resources without regard for location. 

To be precise, A physical or virtualized hardware and software that is hosted as needed on any available resource inside a farm of resources.

What is Cloud Computing?

According to Microsoft Azure, Cloud Computing is the delivery of computing services—including servers, storage, databases, networking, software, analytics, and intelligence—over the Internet (“the cloud”) to offer faster innovation, flexible resources, and economies of scale.

According to Amazon Web Services, Cloud Computing is the on-demand delivery of IT resources over the Internet with pay-as-you-go pricing. Instead of buying, owning, and maintaining physical data centers and servers, you can access technology services, such as computing power, storage, and databases, on an as-needed basis from a cloud provider.

According to Google Cloud Platform, Cloud computing is the on-demand availability of computing resources as services over the internet. It eliminates the need for enterprises to procure, configure, or manage resources themselves, and they only pay for what they use.

According to the National Institute of Standards and Technology (NIST), “Cloud computing is a model for enabling ubiquitous, convenient, on-demand network access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction.”

The NIST defines cloud computing as having five important characteristics: on-demand self-service, broad network access, resource pooling, quick elasticity or extension, and measurable service. It also specifies three “service models” (software, platform, and infrastructure) and four “deployment models” (private, community, public, and hybrid). 

Simply put, it is called “The 3-4-5 Rule”.