Pelvic venous disorder (PeVD) is the modern umbrella term for chronic pelvic pain caused by veins that don't drain properly. You'll also meet the older name pelvic congestion syndrome (PCS) — still widely used, now considered one presentation under the umbrella rather than the whole story.
The umbrella covers three overlapping problems: ovarian vein reflux (valves fail and blood runs backwards into the pelvis), May-Thurner syndrome (a compressed iliac vein) and Nutcracker syndrome (a compressed renal vein). One can cause another, which is why modern work-ups image the whole venous system rather than a single vein.
The renaming matters practically: if your search results and your specialist's letters mix "PCS", "PeVD", "pelvic congestion" and "pelvic venous insufficiency", they're describing the same territory.
Start here: the PeVD overview and what the pain actually feels like.