What is venous disease?

"Venous disease," "varicose veins" and "venous insufficiency" travel together in search results. This page answers the first and sets it beside the other two.
The answer, with its source beside it
The publisher my.clevelandclinic.org defines the term in two sentences. Venous disease is any condition that affects the veins in your body. Veins are flexible, hollow tubes that are part of the circulatory system that moves blood through your body.
Where this question splits from its look-alike
Venous disease is the wide term, and varicose veins and venous insufficiency are the names readers meet when the wording narrows. A reader in Tinley Park who sees all three will do better to compare each publisher's own description than to treat them as synonyms.
Pages to read alongside this one
The Cleveland Clinic page on venous disease is the source of the definition above. The Cleveland Clinic page on varicose veins covers the first look-alike. The MedlinePlus Medical Encyclopedia entry on venous insufficiency covers the second.
The follow-up question
Once the term is defined, the question that follows is how a condition under this wide heading gets checked, which is the testing question answered elsewhere on this site.