Please tell me what an adrenal nodule is?

Adrenal nodule: is a small mass in the adrenal gland. The vast majority of adrenal nodules incidentally detected on imaging studies are benign adenomas. These require no treatment, and generally have characteristic appearances on CT and MRI that enable a confident diagnosis without biopsy. If they don't have these characteristics, they may need follow up or biopsy because neoplasm/cancer is a possibility.