Still confused about those terms ?
Here is a one-word description that summarize it well:
More details with this nice metaphor:
And how does it relate to your IT world ?
IaaS, PaaS and SaaS are three different approaches to cloud-based services, and Microsoft has a strong offering in all, thanks to Azure:
If you are a Visual Studio developer and have not already taken advantage of the Microsoft Azure platform, I encourage you to try and explore its possibilities:
http://azure.microsoft.com (sign-up and get $200 in Azure credit)