Mass Storage Mode - definition
Mobile devices which have expandable memory expansion capability, when are connected with a computer, then, in general, can transfer files over Active Sync or using proper suites. But when the Mass Storage Mode is enabled then the device's built-in memory and expandable memory card acts as an extra storage drive in Windows Explorer or Mac. Files with known or unknown types can be sent or received using Mass Storage Mode. In easier words, enabling Mass Storage Mode means, the device will work as a removable storage device or a simple pen drive.