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.
This cloud model is composed of five essential characteristics, three service models, and four deployment
models.
云计算是一种模型，作用是提供普遍的、便利的、按需的网络访问可配置计算资源池（例如，网络、服务器、存储、应用程序、服务）的能力，
这些资源可以快速分配，投入极少的管理工作或与服务提供商的交互。云计算模型有五个基本的特性，三种服务模型以及四个部署模型。
Essential Characteristics:
On-demand self-service. A consumer can unilaterally provision computing capabilities, such as
server time and network storage, as needed automatically without requiring human
interaction with each service provider.
按需自助服务。用户可以有单方面调配计算资源的能力，例如服务器时间和网络存储，根据需要自动完成而无需人为与服务提供商进行交互。
Broad network access. Capabilities are available over the network and accessed through standard
mechanisms that promote use by heterogeneous thin or thick client platforms (e.g.,
mobile phones, tablets, laptops, and workstations).
宽泛的网络接入。通过标准机制访问网络资源、标准机制用于提升混杂的瘦或胖客户端平台（移动电话、平板电脑、笔记本电脑和工作站）访问
Resource pooling. The provider’s computing resources are pooled to serve multiple consumers
using a multi-tenant model, with different physical and virtual resources dynamically
assigned and reassigned according to consumer demand. There is a sense of location
independence in that the customer generally has no control or knowledge over the exact
location of the provided resources but may be able to specify location at a higher level of
abstraction (e.g., country, state, or datacenter). Examples of resources include storage,
processing, memory, and network bandwidth.
资源池化。提供商的资源池可用于服务多位消费者以多租户的模式，根据用户需求动态分配或预分配不同的物理和虚拟资源。
感觉上是与位置无关的，因为客户通常无法控制或知道资源的精确的位置，但可以在高级别的抽象上指定位置（例如，国家、洲或数据中心）。
资源包括存储、处理器、内存和网络带宽等
Rapid elasticity. Capabilities can be elastically provisioned and released, in some cases
automatically, to scale rapidly outward and inward commensurate with demand. To the
consumer, the capabilities available for provisioning often appear to be unlimited and can
be appropriated in any quantity at any time.
快速伸缩性。 资源能够弹性被提供和下发，在某些情况下，自动的根据需求迅速的向外。向内等量扩展。
对于用户，可以获得资源供应似乎是无限的，可适当的在任何时间使用任意数量的资源。
Measured service. Cloud systems automatically control and optimize resource use by leveraging
a metering capability1 at some level of abstraction appropriate to the type of service (e.g.,
storage, processing, bandwidth, and active user accounts). Resource usage can be
monitored, controlled, and reported, providing transparency for both the provider and
consumer of the utilized service.
可度量服务。云计算系统通过利用改变适用于服务类型的某些抽象层级的度量能力（例如，存储、处理器、带宽以及活动的用户帐户）能够自动控制、优化资源
为服务提供商和消费者使用服务所产生的资源使用需要能够被监控，控制，生成报告。
Service Models: 服务模式
Software as a Service (SaaS). 软件即服务
The capability provided to the consumer is to use the provider’s
applications running on a cloud infrastructure2
. The applications are accessible from
various client devices through either a thin client interface, such as a web browser (e.g.,
web-based email), or a program interface. The consumer does not manage or control the
underlying cloud infrastructure including network, servers, operating systems, storage, or
even individual application capabilities, with the possible exception of limited user specific
application configuration settings.
服务提供商提供运行在云基础设施的服务程序供用户使用，此服务程序可以接受各种客户端设备访问该应用程序，或瘦客户端接口，例如Web浏览器，或程序接口。
消费者并不管理或控制底层的云计算基础架构，包括网络、服务器、操作系统、存储、或甚至应用程序本身，只允许部分受限的用户进行特定的应用程序设置。
Platform as a Service (PaaS). 平台即服务
The capability provided to the consumer is to deploy onto the cloud
infrastructure consumer-created or acquired applications created using programming
languages, libraries, services, and tools supported by the provider The consumer does
not manage or control the underlying cloud infrastructure including network, servers,
operating systems, or storage, but has control over the deployed applications and possibly
configuration settings for the application-hosting environment
服务提供商提供云基础设施，使用户可以在上面部署自己创建或获得的应用程序,这些程序所用到的编程语言、库、服务、工具由服务提供商提供，用户不再管理或控制底层的
云基础设施，包括网络，服务器，操作系统，存储，但是可以管理部署的应用程序，并且可能会配置宿主应用程序的环境。
Infrastructure as a Service (IaaS).基础设施即服务
The capability provided to the consumer is to provision
processing, storage, networks, and other fundamental computing resources where the
consumer is able to deploy and run arbitrary software, which can include operating
systems and applications. The consumer does not manage or control the underlying cloud
infrastructure but has control over operating systems, storage, and deployed applications;
and possibly limited control of select networking components (e.g., host firewalls).
为消费者提供所需的处理器、存储、网络以及其他的基础的计算资源，消费者可以运行部署、运行任意软件，包含操作系统和应用程序。
用户不再管理和控制底层的云基础设施，但可以管理操作系统，存储和部署的应用程序，还能有限制的管理被选择的网络组件（例如，主机防火墙）
Deployment Models:部署模式
Private cloud.私有云
The cloud infrastructure is provisioned for exclusive use by a single organization
comprising multiple consumers (e.g., business units). It may be owned, managed, and
operated by the organization, a third party, or some combination of them, and it may exist
on or off premises.
云基础设施为单一组织的多个用户（例如业务单元）提供专用的服务。它可以由该组织、
第三方机构，或他们的组合来拥有、管理和运营，可能存在于组织内外。
Community cloud. 社区云
The cloud infrastructure is provisioned for exclusive use by a specific
community of consumers from organizations that have shared concerns (e.g., mission,
security requirements, policy, and compliance considerations). It may be owned,
managed, and operated by one or more of the organizations in the community, a third
party, or some combination of them, and it may exist on or off premises.
云基础设施为特定的一些组织的社区用户提供专用的服务，这些组织有共同点理念（使命，安全需求，方针，服从意识)
该云计算基础架构可以由该社区中的一个或多个组织、第三放架构或他们的组合来拥有、管理和运营，它存在于组织内外。
Public cloud. 公共云
The cloud infrastructure is provisioned for open use by the general public. It may be
owned, managed, and operated by a business, academic, or government organization, or
some combination of them. It exists on the premises of the cloud provider.
云基础设施为一般的公众提供专用的服务.该云计算基础架构可以由商业组织、学术组织或政府组织、或者他们的组合来拥有、管理和运营，它存在于云计算服务提供商.
Hybrid cloud. 混合云
The cloud infrastructure is a composition of two or more distinct cloud
infrastructures (private, community, or public) that remain unique entities, but are bound
together by standardized or proprietary technology that enables data and application
portability (e.g., cloud bursting for load balancing between clouds).
云基础设施由两个或更多不同的云基础设施（私有、社区或公有）组成，它们之间有独立的实体，但通过标准或专有技术绑定在一起，实现数据和应用程序的可移植性（负载均衡的云爆发）。
文章来源:http://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-145.pdf