A cloud is a distinct and remote IT environment designed for the purpose of remotely provisioning scalable and measured IT resources. In order to remotely provision scalable and measured IT resources in an effective manner, an IT environment requires a specific set of characteristics. These characteristics need to exist to a meaningful extent for the IT environment to be considered an effective cloud.

• On-Demand Usage – This characteristic allows for the usage of self-provisioned IT resources to be automated so that no further human involvement by the provider or consumer of these resources is required.
• Ubiquitous Access – This is the ability for a cloud-based IT resource to be widely accessible.
• Multitenancy – Multitenancy is the characteristic of a software program that enables an instance of the program to serve different consumers (tenants), each of which is isolated from the other.
• Elasticity – This is the ability of a cloud to enable its consumers to scale cloud-based IT resources up or down, as required.
• Measured Usage – This is the ability of a cloud platform to keep track of the usage of its IT resources by its consumers.
• Resilient Computing – This characteristic represents a form of failover that distributes redundant implementations of IT resources across physical locations.

Services that reside in cloud environments are referred to as cloud services or  cloud-based services. Services are one form of IT resource hosted by clouds.