Availability Zones is a high-availability offering that protects your applications and data from datacenter failures. Availability Zones are unique physical locations within an Azure region. Each zone is made up of one or more datacenters equipped with independent power, cooling, and networking. To ensure resiliency, there’s a minimum of three separate zones in all enabled regions. The physical separation of Availability Zones within a region protects applications and data from datacenter failures. Zone-redundant services replicate your applications and data across Availability Zones to protect from single-points-of-failure.
Azure services that support Availability Zones fall into two categories:
Zonal services – you pin the resource to a specific zone (for example, virtual machines, managed disks, IP addresses), or
Zone-redundant services – platform replicates automatically across zones (for example, zone-redundant storage, SQL Database).
To achieve comprehensive business continuity on Azure, build your application architecture using the combination of Availability Zones with Azure region pairs. You can synchronously replicate your applications and data using Availability Zones within an Azure region for high-availability and asynchronously replicate across Azure regions for disaster recovery protection.
Infrastructure as a Service (IaaS) – servers, storage, network and operating systems – as an on-demand service. Rather than purchasing servers, software, datacenter space or network equipment, clients instead buy those resources as a fully outsourced service on demand.
Platform as A Service (PaaS ) can be defined as a computing platform that allows the creation of web applications or software quickly and easily and without the complexity of buying and maintaining the software and infrastructure underneath it.
Software as a Service (SaaS) is software that is deployed over the internet. In a SaaS you are provided access to application services installed at a server. You don’t have to worry about installation, maintenance or coding of that software. An obvious example of SaaS is Microsoft’s Office 365, where the applications run remote from the user’s computer.
Watch this video. I like his style of explanation: