There are a lot of opinions and implementations of "the cloud". There are multiple companies that offer it, and multiple ways to use it, some correct, some incorrect, but for our purposes here we are going to give an overview of the cloud and what it is.
So what is it?
If you've been in IT, and if you've been at any company of any size, you've probably seen the "server room." It's normally a big room that's kept fairly cool and houses a lot of machines that run hot. This is your on premise server room, data center, whatever the term you'd like to use. It's normally a single location, and because of that it can be a liability from an, "always on", perspective.
In it's simplest term, the cloud is nothing more than what I just described. It's a data center, the difference is the redundancy capabilities, the availability, and the security of this data center dwarfs what most IT can do on premises. That's not to say that some companies don't still have their entire infrastructure housed within their four walls with some redundancy happening in an offsite DC. In fact many do, but where the power of the cloud can be used, the world of the IOT (Internet of things) opens up.
If I'm on premises and a nationally syndicated program runs a commercial about our flagship product and the hits to our website or ordering system spike dramatically, I run the risk of the systems going down from too much influx of traffic. However, if in the cloud, running an application that takes advantage of the ability of the cloud to scale with demand, the user would see very little impact and the only thing we as a company would get is a larger bill from whatever cloud service we happened to be using.
The beauty of the cloud is that is can scale up, and then scale back down, if the developers and architects have built the proper patterns and growth ratios. Our team once created a visual representation of a cloud noSQL data store scaling both up, and out. It was like we were watching the machine's breathe. At that time we'd never seen such power and such opportunity, and we were hooked.
All that to say, coding for the cloud takes a different consideration and toolkit, and each of the different services (AWS Amazon, Microsoft Azure, or Google's Suite) off their own unique implementations and nuances (some good and some bad) but the ability to seamlessly scale up processing power, memory, storage without having to install any hardware or VMs in an instant is a brave net world indeed.