This option is displayed only if a text layer is present.

When you add text to an image, GIMP adds specific informations. This command lets you discard these informations, transforming the current text layer into a normal bitmap layer. The reason to do that is not evident.

Note that this transformation of text into bitmap is automatically performed when you apply a graphic operation to the text layer. You can get text information back by undoing the operation which modified the text.