Ayya is a Pali word, translated as "honourable" or "worthy" or "venerable lady." It is most commonly used as a veneration in addressing or referring to an ordained female Buddhist nun, most often of the Theravadin tradition in southeast Asia. Ayya can refer to either a bhikkhuni (fully-ordained and usually wearing orange or yellow robes in southeast Asia) or a samaneri (shramanerika) 10 precept novice renunciant or a sikkhamana (wearing white, brown or sometimes pink), but not to non-ordained precept holders.
Generally for bhikkhunis, robes would be maroon with yellow in Tibet; gray (for Mahayanans) or orange/yellow (for Theravadins) in Vietnam; gray in Korea; gray or black in China and Taiwan; black in Japan; orange or yellow in Thailand, Sri Lanka, Nepal, Laos, Cambodia and Burma. The color of robes distinguishes both level of ordination and tradition, with white (usually worn by a male renunciant before ordination) or pink symbolising a state of ambiguity, being on the threshold of a decision, no longer secular and not yet monastic.
See also: Bhikkhuni ordination