There are two primary deployment models of the cloud : Public and Private.
Public Cloud : The set of hardware, networking, storage, services, applications, and interfaces owned and operated by a third party for use by other companies or individuals is the public cloud. These commercial providers create a highly scalable data center that hides the details of the underlying infrastructure from the consumer. Public clouds are viable because they offer many options for computing, storage, and a rich set of other services.
Private Cloud : The set of hardware, networking, storage, services, applications, and interfaces owned and operated by an organization for the use of its employees, partners, or customers is the private cloud. This can be created and managed by a third party for the exclusive use of one enterprise. The private cloud is a highly controlled environment not open for public consumption. Thus, it sits behind a firewall.
Hybrid Cloud : Most companies use a combination of private computing resources and public services, called the hybrid cloud environment.
Multi-Cloud : Some companies, in addition, also use a variety of public cloud services to support the different developer and business units – called a multi-cloud environment.