Kyai
A Kyai (key-eye) is an expert in the religion of Islam. The word Kyai is of Javanese origin. Traditionally, students of Islam in Indonesia would study in a boarding school. The leader of the school was called Kyai, roughly meaning teacher in the Javanese language. This is similar in nature to western Christians addressing a Catholic Priest as Father, and would be followed up with the person’s name. (E.g. Kyai Abdul is used in the same way as Father Smith). The traditional word for a teacher in Islam is ustdat (oos-dat) which is from the arabic word. There are many ustdat in Indonesia who teach the religion, but do not have a boarding school.
Some Indonesians refer to a high-level or widely regarded Kyai as an Ulama. This word actually is the plural form of the Arabic word alim which means knowledgeable person. A group of alim are referred to as ulama. For example, there is one alim in the room, but there are three ulama outside. Through common usage in Indonesia, the word ulama grew to signify a high level Kyai, even though this is a grammatical misuse of the word in Arabic. A person who is referred to in this way would seldom introduce themselves as an ulama. Two possible reasons for this are 1. to avoid being arrogant, and 2. because the speaker, as a well-educated Islamic teacher, knows that the word ulama is a plural form of alim.
A Kyai would normally set up his own boarding school called a Pondok Pesantren literally meaning boarding house in Indonesian language. A student in the school is called a santri. A child of a Kyai, or a main student, may take over the supervision of the school upon the death of the original founder, and would then be called Kyai. It is possible for one boarding school to have numerous Kyai living and teaching there, if the school is large. In general most schools have a modest size of a few hundred students and only one person who is called Kyai. The other teachers in the school would be called Ustdat. In fact, ustdat and kyai mean the same thing but in reality, many Indonesian Muslims consider a kyai to be higher ranked, generally because a kyai would run his own boarding school.