A nodule means a mass, usually a solid nodule with a hard texture, which may be benign or malignant, and is usually more common on the surface of the body, such as sebaceous cysts, thyroid nodules, and breast nodules. A sebaceous cyst is a hard, tofu-like mass formed when the sebaceous gland is blocked, and is prone to abscess formation secondary to bacterial infection. Benign nodules are mainly thyroid adenoma and nodular goiter, while malignant nodules are thyroid cancer, which requires ultrasound examination to determine the benignity and malignancy of the nodule. If the nodule is considered malignant, radical thyroid cancer surgery is required; if it is benign, smaller nodules can be followed up, while larger nodules can be removed surgically. If a nodule appears in the breast, it may be a fibroadenoma, a mass of breast enlargement, or a breast cancer, which can be detected by ultrasound or mammogram. If the nodule is malignant, a modified radical breast cancer surgery is needed; if it is benign, small nodules can be followed up, but large nodules need surgery.