The Android OS is a mobile device operating system developed by The Open Source Alliance specifically for the mobile device environment. The Android OS is similar to the way the iPhone OS works with widgets and icons on the home screen. A few things that make the Android different than the iPhone OS is OSX will only run on an iPhone. Whereas the Android OS will work on a variety of smart phones made by a variety of manufacturers. The advantage of here is if you do not like a specific handset, and want an Android OS you can choose a different one by a different manufacturer. Another difference is you can literally write your own program to run on an Android handset. Where with devices that run other OS's you can only use what the software vendor approves.
One thing iPhone and Android share is both OS's have their roots in the former Bell Labs (Now AT & T and Verizon due to a forced divestiture that occurred in the 1980s.) It all started with the UNIX OS. In 1975 the UNIX OS was made available outside of AT & T to educational and research institutions due to a US Federal law prohibiting AT & T from sales of products due to its unique monopoly status, and as a result was made available at no costs. In this stage Unix saw itself splitting into various flavors. Two of which will be covered next.
Fast forward to today, the UNIX platform has evolved through different paths The two of the most well know of these is, the Mac OS, and the Linux OS. Mac is a Unix based OS that only runs on Apple products and Linux is an Open Source OS that will run on just about anything out there. The Open Source nature of it makes the code public and anyone who can improve upon has the right to do so as long as they share the changes that they made.
One of the largest partners to the Open Source Alliance in bringing Android to market is Google. Google's servers all run on Linux. Many in the IT world will tell you Linux is far superior to its Windows counterparts, when it comes to running servers. The main thing that kept Open Source software out of the market was it lacked marketing efforts, and ease of use. Whereas Apple built there brand on, marketing and, ease of use, and in order for the Linux kernel to gain popularity it had to be marketed, which is what Google brings to the table and gain ease of use which is what the Android platform engings . The biggest advantage to Android is you can make it just about anything you want.