Windows Azure is Microsoft’s public cloud computing platform. It’s a place to run your applications out on the internet, at scale. With geographically distributed datacenters worldwide, applications can be built, hosted and managed around the world. With Windows Azure, you can extend and even move your datacenter services off-premises or beyond a hosted environment, paying only for the resources you use at any given time. The flexible cloud computing platform of Windows Azure lets you focus on solving business problems and addressing customer needs, not on the infrastructure.
Benefit
Only Microsoft delivers a comprehensive, end-to-end cloud solution that is designed so your private cloud and public cloud work together. With Microsoft, the investments you make today will work for you in the future.  Microsoft’s Public Cloud Platform delivers the following benefits

A Powerful and Practical Platform
You don’t need to learn new tools or a new platform to harness the benefits of cloud computing. With Windows Azure, you can easily move existing applications to the cloud and create new applications and services using technology you already know and trust.

Flexibility
Windows Azure gives you the agility to take advantage of multiple application development tools, automated service management, and global datacenter presence.  This enables you to respond faster to customer needs, focus on your competitive differentiators, and reach new markets.

Freedom to Choose
With Windows Azure you have the freedom to choose where and how you manage, deploy, and store data, so that you can focus on business challenges and customer needs.

Simplified Approach
With Windows Azure, you can create and manage applications and services utilizing familiar languages such as .NET, Java, PHP and Ruby.

Reliable Solution
Cloud computing from Microsoft means 99.9%+ uptime and 24/7 support so you can be sure you’ll have the services your business needs whenever it needs them.
Ref :http://www.microsoft.com/en-us/server-cloud/public-cloud/default.aspx