Livedo reticularis: This lacy line/mottled appearance on the skin is a clinical finding. It may or not be related to underlying diseases. The most important one of these is the presence of lupus anticoagulant in blood or cholesterol embolism.

It is often seen as an insignificant finding in young females. Other  vasculitides too can have this like SLE, Scleroderma, RA, Wegener's, Raynaud's etc.

By itself livedo is not a disease but is an indicator to the possibility of the above mentioned.