The cloud term is normally referred to a service which is accessible by everyone on the internet, it is also known for its high availability and to prevision resources to the cloud on demand.
In essence the cloud is a cluster of dedicated servers that ensures the services running on the cloud remain online and accessible at any given time regardless of the situation. Through the usage of redundancy and double links on the network level, one can ascertain a certain level of cloud infrastructure and ensuring the services to be operational.
The cloud comes in many shapes and forms. It can be in the way of online websites or can be in the form of online streaming services. With most cloud services you can grow the cloud on demand, this is usually done by adding resources to the cloud itself in the form of hard drive capacity or processing power as the services can be added in whist the service is in operation, this is known as hot adding or hot services.
Adding resources on demand is particularly useful for peak season sales such as Christmas or for promotional periods where by sales may be higher. Most clouds allow hourly rate billing thus ensuring your services remaining online.