What is Magento?
Magento is the most widely used ecommerce platform in the world. It is built in PHP and uses open source code.
Magento was first released in 2008 by a company called Varien. The developers at Varien designed a modular extendible architecture which made the platform very flexible and ultimately a very powerful tool. Magento's extensive use of design patterns and good practices made Magento stand out from the crowd compared to other PHP platforms.
Over the years Magento has gained a large following from the open source community who contribute to the framework and help add features not available in the core codebase.
Currently, in my opinion Magento is still the best ecommerce option available and with Magento2 just being released it looks like Magento will stay as number one.