I had two ultrasounds of my lower extremities and the arterial vascular sonogram stated this. " hemodynamically significant stenosis " what does this mean? i'm worried?

It means that artery is partially blocked with possibly impaired circulation. You need to see vascular surgeon for a complete evaluation.

Usually this means you have a "narrowing", often from atherosclerotic plaque, that results in some decrease in blood flow past that level. If you had symptoms such as "claudication" (cramping pain while walking), or pain in leg while resting; Or prior surgery, which prompted the study, then I'd consult with a vascular surgeon who would probably recommend an angiogram which shows better detail.