Wikipedia
A bhikkhunī ( Pali) or bhikṣuṇī ( Sanskrit) is a fully ordained female monastic in Buddhism. Male monastics are called bhikkhus. Both bhikkhunis and bhikkhus live by the Vinaya, a set of rules. Until recently, the lineages of female monastics only remained in Mahayana Buddhism and thus are prevalent in countries such as Korea, Vietnam, China, and Taiwan but a few women have taken the full monastic vows in the Theravada and Vajrayana schools over the last decade.
In Buddhism, women are as capable of reaching nirvana as men. According to Buddhist scriptures, the order of bhikkhunis was first created by the Buddha at the specific request of his aunt and foster-mother Mahapajapati Gotami, who became the first ordained bhikkhuni. A famous work of the early Buddhist schools is the Therigatha, a collection of poems by elder nuns about enlightenment that was preserved in the Pāli Canon.
Bhikkhunis are required to take extra vows, the Eight Garudhammas, and are subordinate to and reliant upon the bhikkhu order. In places where the bhikkhuni lineage was historically missing or has died out, due to hardship, alternative forms of renunciation have developed. In Tibetan Buddhism, women officially take the vows of śrāmaṇerīs (novitiates); Theravadin woman may choose to take an informal and limited set of vows similar to the historical vows of the sāmaṇerī, like the maechi of Thailand and thilashin of Burma.