Cloud computing is a metaphor for a system designed and maintained by the service provider where servers house data and applications. Accessible remotely via a secure connection eliminating the need for the end user to purchase, maintain, and power the physical infrastructure that houses this data.
Refers to something that is remote (available via the Internet)
There are 3 basic layers of cloud computing:
Infrastructure as a service generally provides virtualized servers, networks, storage and system software designed to enhance or replace the functions of entire data centers (the actual servers, routers, memory, wires, etc.)
Platform as a service provides virtualized servers where users can run and develop applications without the need to purchase or maintain the operating systems and hardware that are needed to run these applications (such as Windows, Linux, Apple platform) platform is generally an operating system
Application: Software as a service delivers user software over the internet eliminating the need to install these applications on the customers own computer simplifying maintenance and support (Oracle, AS400, etc.)
Storage as a service provides clients the ability to store their data via the internet so for storage and disaster recovery management.
Fast start up: the ability to be able to be up and running in a short time frame as opposed to the traditional need to purchase hard ware install software test and debug. The computing power is there when you need it.

Scalability: the ability to handle increased volume needs without the need to purchase more hardware. It’s easy to grow or shrink to match you demand.
Accessibility: the ability to access data, applications, more computing power and space from a wide range of products and places, from laptop, smart phone, home based office or workplace network.
Cost efficient: Without the need to maintain the physical data centers the energy and the people to maintain and support them you reduce the cost of operating them. Paying only for what you use.
Cons:
Reliability: a misconception about cloud hosting is that the data and apps are housed “in a cloud in the sky not in a data center” which is not true cloud hosting resides in a single data center so when there is a failure this becomes a huge liability. There have been instances where for example Facebook has a problem and users are unable to log in.
Security: we all know that the internet has many security issues and cloud computing includes most of those issues. Keeping your data safe is very important. Because the responsibility of securing your data is taken out of your hands you’re depending on an external organization to handle the security and security can become a big concern.
Speed: because the applications you’re running are not physically installed on your computer there is a lag between the connection from the end user and the speed is based on the speed of your connection
Requires constant connection: because you have to connect to the cloud provider your connection has to be up and running at all times to able to use the service where as if you had the applications stored on your computer and your connection was lost you would not lose the service
Schools may be able to minimize unnecessary such as installation of a physical data center, maintenance of servers, upgrades when needed, training of IT people, etc.
Another benefit in using cloud computing with education is that depending on the project(s) which are being worked on – that amount of room so to say is available. Remember, it can be either expanded or minimized as the need demands it. It is also available on demand; therefore, making it easily accessible with no need to wait for upgrades.
Collaboration can be made easier with cloud computing because as long as each person as access to the internet, they may be able to work on the same projects from anywhere and anytime. (from home, from school, etc.) This can be useful to students because they will have the support from teachers and students in case the need for support arises.
http://www.youtube.com/watch?v=ae_DKNwK_ms&feature=player_embedded