It is one that affects a number of organs and tissues, or affects the body as a whole.
In lupus, something goes wrong with your immune system, which is the part of the body that fights off viruses, bacteria, and germs (foreign invaders, like the flu). Normally our immune system produces proteins called antibodies that protect the body from these invaders. These autoantibodies cause inflammation, pain, and damage in various parts of the body. Lupus is also a disease of flares (the symptoms worsen and you feel ill) and remissions (the symptoms improve and you feel better). Lupus is a chronic, autoimmune disease that can damage any part of the body (skin, joints, and/or organs inside the body). Chronic means that the signs and symptoms tend to last longer than six weeks and often for many years. These autoantibodies cause inflammation, pain, and damage in various parts of the body. Lupus is also a disease of flares (the symptoms worsen and you feel ill) and remissions (the symptoms improve and you feel better). This is a list of systemic diseases with ocular manifestations. An ocular manifestation of a systemic disease is an eye condition that directly or indirectly results from a disease process another part of the body. There are many diseases known to cause ocular or visual changes.  Post 3. @SarahGen-- Diabetes is a metabolic disorder but it is also a systemic disease because it affects many different systems in the body. For example, uncontrolled diabetes will cause complications in organs like the liver and kidneys and systems like the central nervous system. Autoimmune disease is another type of systemic problem, though again this category can be wide ranging. Some common examples of autoimmune conditions are HIV/AIDS, Celiac disease, and Multiple Sclerosis. Lupus is an autoimmune disease. This means that the body's natural defense system (immune system) attacks healthy tissues instead of attacking only things like bacteria and viruses. This causes inflammation.  Systemic diseases are diseases that involve many organs or the whole body. Many of these diseases also affect the eyes. In fact, an eye exam sometimes leads to the first diagnosis of a systemic disease.  DESCRIPTION. The hands, being composed of many types of tissue, including blood vessels, nerves, skin and skin-related tissues, bones, and muscles/tendons/ligaments, may show changes that reflect a disease that affects other parts of, or even the whole body. These are known as a systemic diseases A systemic disease is one that affects a number of organs and tissues, or affects the body as a whole. Signs of a systemic disease may be evident on the outer surface of the eye (eyelids, conjunctiva and cornea), middle of the eye and at the back of the eye (retina).. Since 500 B.C., some researchers have also believed that the physical condition of the fingernails and toenails can indicate various systemic diseases. Lupus is a chronic inflammatory disease that occurs when your body's immune system attacks your own tissues and organs. Inflammation caused by lupus can affect many different body systems — including your joints, skin, kidneys, blood cells, brain, heart and lungs. 
http://www.lupus.org/answers/entry/what-is-lupus http://www.lupus.org/answers/entry/what-is-lupus https://en.wikipedia.org/wiki/List_of_systemic_diseases_with_ocular_manifestations http://www.wisegeekhealth.com/what-are-the-different-types-of-systemic-disease.htm http://www.webmd.com/lupus/tc/lupus-systemic-lupus-erythematosus-topic-overview http://chicago.medicine.uic.edu/cms/One.aspx?pageId=15427346 http://www.assh.org/handcare/hand-arm-conditions/systemic-diseases https://en.wikipedia.org/wiki/Systemic_disease http://www.mayoclinic.org/diseases-conditions/lupus/basics/definition/CON-20019676
what is systemic disease