Thyroid cysts generally refer to a cystic mass found in the thyroid, typically containing a mixture of fluid or semi-solid fluid. The mass usually has clear boundaries and is painless. It can move up and down with swallowing, which distinguishes it from some subcutaneous nodules. Thyroid cysts generally do not show obvious symptoms or clinical signs and are mostly discovered when looking in the mirror or during a physical examination. However, larger thyroid cysts may cause compression symptoms, such as pressing backward against the trachea or esophagus, leading to symptoms like breathlessness and discomfort swallowing. A small portion may also exhibit signs of thyroid dysfunction, such as hyperthyroidism or hypothyroidism, although this is relatively rare in clinical settings.