With Software as a Service (SaaS), the user has access to the application, which is made available fully functional by the provider – no operation, no customization, just interaction with the finished application. Just think of Gmail.
At the other end of the cloud spectrum is Infrastructure as a Service (IaaS): The user receives virtualized hardware resources – servers, networks, storage – and can install and control the operating system, middleware, data and applications running on them. This means that more components of the environment are customizable, but it also means that there is an obligation to select, install, operate and maintain what requires knowledge, time and personnel. IaaS is for example offered by Amazon Web Services (AWS), Microsoft Azure, and Google Compute Engine (GCE).
The model in between is called Platform as a Service (PaaS) and allows users to develop their own applications and deploy them in a cloud infrastructure. The tools and infrastructure for this are made available by the provider.
Hmm, sounds great, but I can’t do cloud right now …
If you need to postpone your move to the cloud, but still want to take advantage of modern technology, here are some ideas: