Due to the absence of a standard usage for individual icons, text labels are necessary to communicate meaning and reduce ambiguity in an icon-based design.
They are road signs for your daily rituals — the instantly recognized symbols and icons you press, click and ogle countless times a day when you interact with your computer. But how much do you know about their origins?
Developing Windows 8 – Using AppBarCommand Icons outside the AppBar « Matt Duffield
One of the things I really like about developing Windows 8 applications is the ability to use the built in icons provided by the Segoe UI Symbol font.