Windows Azure is a cloud based hosting service provided by Microsoft.
Azure is a complete cloud platform that can host your existing applications, streamline the development of new applications, and even enhance on-premises applications. Azure integrates the cloud services that you need to develop, test, deploy, and manage your applications—while taking advantage of the efficiencies of cloud computing.
By hosting your applications in Azure, you can start small and easily scale your application as your customer demand grows. Azure also offers the reliability that’s needed for high-availability applications, even including failover between different regions. The Azure portal lets you easily manage all your Azure services. You can also manage your services programmatically by using service-specific APIs and templates.
You can read more about Microsoft Azure and its services, here.