When I begun studying for my AZ-900 I struggled getting this concepts and could often get them mixed up but after writing this blog I feel more confident in explaining them to others. I hope you feel the same after reading it.
I'll be sharing more insights on the cloud service models and there key differences.

Microsoft Azure is a Cloud computing platform and an online portal that allows people to access and manage cloud services and resources provided by Microsoft.

• Cloud Computing : the delivery of computing services over the internet, which is otherwise known as the cloud. These services include servers, storage, databases, networking, software, analytics, and intelligence.

Cloud Service Models define the different level of shared responsibility that a cloud provider and cloud tenant are responsible for.There are 3 Cloud Service Models:

• Infrastructure as a Service(IAAS)
• Platform as a Service (PAAS)
• Software as a Service (SAAS)

Infrastructure as a ServiceThis model is the closest to managing physical servers. A cloud provider keeps the hardware up to date, but operating system maintenance and network configuration is left to the cloud tenant.
Example Azure virtual machines are fully operational virtual compute devices running in Microsoft data centers.

Platform as a ServiceThis model is a managed hosting environment. The cloud provider manages the virtual machines and networking resources, and the cloud tenant deploys their applications into the managed hosting environment.
Example Azure provides app services supporting the entire building process of a web app development and deployment,

Software as a ServiceIn this cloud service model, the cloud provider manages all aspects of the application environment, such as virtual machines, networking resources, data storage, and applications. The cloud tenant only needs to provide their data to the application managed by the cloud provider.
Example Microsoft Office 365 provides a fully working version of Microsoft Office that runs in the cloud.

An illustration of the various levels of responsibility between a cloud provider and a cloud tenant.