A ribbon is an interface with set of toolbars placed on several tabs.
A ribbon is a set of toolbars placed on several tabs. It is a technique used by Microsoft and was released in the Office 2007 version. Since 2007 the ribbon have the standard interaction container in Microsoft products. An example of the ribbon:
Questions having the ribbon tag refers to design and development of the ribbon.
More to read: http://en.wikipedia.org/wiki/Ribbon_(computing)