A cyst is a sac filled with liquid or semisolid material that forms under the skin or somewhere inside the body. The Bartholin's gland is one of two small glands on each side of the labia minora, just outside of the opening to the vagina. During sexual arousal, the Bartholin's gland releases a lubricating fluid. A Bartholin's gland cyst develops when the gland becomes blocked. The Bartholin's gland can become blocked for a variety of reasons, such as infection, inflammation or long-term irritation.