What exactly do "scalable hosting" and "elastic hosting" mean? Some hosting companies seem to use both terms interchangeably.
That's because they are interchangeable, for the most part. It just means that you can use and pay for only the resources you need. If you need more resources, you pay for more and are allocated that amount. It's scalable in that you can expand your hosting requirements, and elastic in that you can reduce your hosting requirements. For the most part, it's a lot of marketing fluff, but that's the general idea.