What is a cyst exactly and what to do if i have one on my kidney?

Cyst: Cyst just referrers to a pocket of empty space in the kidney. Think of it as a hollow ball inside the kidney. It may or may not be concerning. It is normal to have what are called "simple cysts" up to a certain number, as you age. The imaging report should comment on whether the cyst is simple vs complex, and whether the kidney architecture is abnormal.