It's a functionality update that'll bring native Android support for fingerprint scanning for security, Android Pay for mobile payments, and support for USB-C, the new standard that will replace microUSB for charging and connecting to other devices.
Apart from the added functionality, Android users should find that Android 6.0 Marshmallow will look and feel very familiar, as not much about the interface is being changed.
The last version of Android (5.0), called Lollipop, couldn't support any of these features, which was a limiting factor for some Android phone makers who wanted to compete with Apple's iPhones, especially when it came to fingerprint scanning.
You'll find fingerprint scanning in a few Samsung phones because they incorporated it into their own layer of software, called TouchWiz, that runs on top of Android.
Now, any Android phone with a built-in fingerprint scanner can make mobile payments and unlock with your fingerprint. That included Google's own Nexus line of smartphones and tablets, which are rumored to feature both fingerprint scanning and USB-C.
Support for USB-C will also help phone makers adopt the new standard more readily, which can charge your phone faster than microUSB, as well as connect more easily to other devices, like an HD TV.
Android Pay is almost identical to Apple Pay in that it uses near-field communication (NFC) to make mobile payments.