The "Cloud" is often referred to as the "Internet" because it is a web of interconnected devices such as servers in a datacenter sharing data and other services over the internet.

Cloud computing offers a range of computing resources that Service providers deliver to customers via the internet. It is simply the provision of Infrastructures, services that enable businesses to build, deploy or use applications over the cloud in a scalable, efficient and Pay-as-you-go manner.

For a formal definition, Cloud computing is the on-demand availability of computer resources, especially data storage and computing power, without direct active management by the user. The goal here is to help businesses achieve economies of scale.
Cloud computing has been around since the 2000s and has technology would have it, cloud computing keeps evolving to solve potential business or computing challenges through innovation and host of competing cloud service providers.
Now that we know what cloud computing is about. Let's dive a bit into the models through which these services are delivered to customers.

Cloud computing delivers services through two models: the Service Model and Deployment Model.

Cloud Service Model: The most common and widely used cloud computing services are Infrastructure as a Service (Iaas), Platform as a Service (PaaS) and Software as a Service (SaaS).

Infrastructure as a Service (Iaas): IaaS is the most basic form of cloud computing service. With IaaS, computing architecture and infrastructure (servers, virtual machines, storage, and networking and firewall security ) are virtually provisioned to the customer or client. On this underlayer, the customer installs, configure, and manages their software - operating systems, middleware, and applications. Customers do not have to worry about IT infrastructure.
Benefits are: this is very helpful in a High-performance computing environment, for faster setup of the Test and Development environment, and to host Web apps quickly. The target customer here is the IT administrator.
Some IaaS providers include Amazon Web Services - EC2 (Elastic Cloud Computing), Cisco Metapod, Microsoft Azure, Google Compute Engine, Heroku, DigitalOcean, and Rackspace.

Platform as a Service (PaaS): The cloud service provider provides a platform allowing customers to develop, run and manage applications with no complexity of building and maintaining the infrastructure. IT resources provided include Networks, servers, and storage, Operating systems, and databases. The customer is provided with hardware and software(Operating system (Windows, Linux) environment, programming language support, frameworks, etc) tools, that enable rapid application development.
Benefits are: shorter coding time, increased time of development and deployment, scalability, and more resources can be released as the application grows. The providers perform all the latest component updates and security patches, thus, your application runs on the latest technologies. However, I will advise customers using PaaS to perform regular backups and ensure data security. The target customer here are Software developers.
Some PaaS providers include Amazon Web Service - Elastic Beanstalk, Google App Engine, RedHat Openshift, and Microsoft Azure.

Software as a Service (SaaS): SaaS providers lease application software to clients. The cloud service provider hosts the application, manage the infrastructure, run maintenance, software upgrade, and security patches. The client access the service, through the web browser, independent of any platform, and over the internet. The software is licensed on a subscription basis to the customers. There is no need for any installation.
Benefits are: the platform is universally accessible, allows multi-tenancy, provides modest software tools and users can work collaboratively. The target customer here are End-users.
Some SaaS providers include Google Apps (Gmail, Google Drive), Office tools (Google Docs and Microsoft Office365), customer relationship management software (Salesforce), and so on.

Let's look at the Deployment model of cloud computing.

Cloud Deployment Model: The most common and widely used cloud computing services are Public cloud, Private cloud, and Hybrid cloud. Cloud deployment models show how cloud services are made available to users. You must choose a model that meets your business objectives. Each model solves a particular business need through its value offerings and cost. Choices should be made based on informed decisions guided by the following; business goals, cost of deployment and management, infrastructure requirement and data security and privacy. Now let's discuss each model.

Public cloud: The cloud provider maintains the hardware and computing infrastructure that an organization needs for free or at a specific cost with the possibility of scaling up when more resources are needed. This model is available to all users who want to make use of computing resources. Public cloud lowers capital expenditures for servers and other computing infrastructure.
The benefits are Scalability, little or no downtime(24/7 operation), cost-effectiveness, uncustomized environment that is readily available. However, the public cloud model is less secured compared to other deployment models. One's choice depends on the objective of the business. If privacy and security are not paramount, Public cloud may seem like a good option.

Private cloud: Private cloud is a good option for any organization that security and privacy are paramount. It is most suitable for a large Enterprise-level organization that can pay for the very expensive cost. That is why this secure, flexible computing deployment model is not a choice for small to medium-sized enterprises. The private cloud model offers more controlling abilities over the resources. Computing services are provisioned over private IT infrastructure for the dedicated use of a single organization.
The benefits are Storage and network components that can be customized, a high level of control over corporate information, and a high level of security, privacy, and reliability. The most significant disadvantage of the private cloud model is the high-cost intensiveness in acquiring and maintaining the IT infrastructure.

Hybrid cloud: As the name suggests, a hybrid cloud is a combination of public and private cloud best offerings. Organizations can use a private cloud for running confidential and critical operations and use the public cloud for sharing workloads and scale the infrastructure.
The Benefits are; High level of scalability and flexibility, High level of security, privacy, and reliability, and Relatively affordable cost.

Cloud computing provides near-instant access to as many computing resources as you want when you need it along with the ability to obtain computers with a specific configuration. Also, scalability, fast product or service delivery and greater IT efficiencies are benefits of cloud computing. Organizations should carefully consider their choice of a cloud service and deployment model that best suit the business objectives.