A cloud is called a "Public Cloud" when the services are rendered over a network that is open for public use. Unified Communications as-a-service (UCaaS), Contact Center as-a-service (CCaaS) and Conferencing as-a-service (CaaS) are commonly deployed over public clouds. However, if security or compliance are important, alternative options may make better sense from a deployment perspective.
Private cloud is a cloud infrastructure operated solely for a single customer or organization. However, these can be managed internally or by a third party and hosted either internally or externally. Due to the nature of latency sensitive voice and video applications, this can be a very good option for larger customers to deploy UCaaS, CCaaS and CaaS solutions. However, these solutions generally take more resources and are not as cost-effective as public cloud solutions.
Hybrid Cloud is a composition of two or more clouds that remain distinct entities but are bound together, offering the benefits of multiple deployment models. Hybrid Cloud can also mean the ability to connect colocation, managed and/or dedicated services with cloud resources. For mid-sized and enterprise customers, these tend to offer better security, compliance and choice over more commonly deployed public or private cloud UCaaS, CCaaS and CaaS solutions.