Nodules are small, rounded lumps that can form in various parts of the body, including the skin, lungs, and thyroid gland. They can be solid or filled with fluid and vary in size. Nodules may be benign, meaning they are not harmful, or malignant, indicating the presence of cancer. In the lungs, for example, pulmonary nodules can be detected through imaging tests like X-rays or CT scans. While many nodules are harmless and require no treatment, some may need further evaluation to determine their nature and whether any action is necessary.