A cloud web hosting service means that each part of your web presence will be maintained by a separate server. For example, your files and databases will be maintained by different machines and since only one kind of processes will run on a server, every single machine will perform better and will use its resources to the fullest. Whether you will get a real cloud service or not also depends on the control panel that you will use to manage your account. Since most control panels were made to operate on a single server, they are unable to work on a cloud platform whatever a given Internet hosting provider may advertise. In case one service stops responding, the whole server could go down, so your sites will not be accessible. That's why you should check what service you will actually receive if you are looking for cloud hosting before you buy anything.
