Corpus luteum, an endocrine gland in mammals, has many synonyms. It is also called yellow body, lutein gland, and corpus rubrum. This gland develops from the ruptured ovarian follicle, and it secretes a hormone called progesterone. During pregnancy, it maintains the development of the uterine lining and prepares it for the implantation of the fertilized egg. In some cases, the corpus luteum can form a cyst, which is known as corpus luteum cyst. This is a common occurrence in women of reproductive age and is usually not harmful. Understanding the synonyms of the corpus luteum helps to recognize this important gland in the body's reproductive system.