A type of
mountain bike specific
mudguard. Both
front and
rear versions are available. Designed to stop the dreaded
crud fouling up your cables and spraying up into your face.
The latset version for your rear wheel has a new, more complicated fitting, which invlolves connecting fiddly stays to your mudguard eyes and the mudguard itself. The older, and in my opinion superior, design had a simple bracket which attached to the seatpost of your bicycle.