What is the difference between polycythemia, polycythemia rubra vera and polycythemia vera?

Polycythemia: Polycythemia is a terminology used for a condition where your hemoglobin is elevated above the normal range.It does not tell you what the cause of the condition- which could be caused by a primary bone marrow problem -( which is called polycythemia rubra vera -abbreviated as polycythemia vera) vs some other secondary conditions such as chronic lung problem, sleep apnea, liver mass/renal mass et.