This is by no means an exhaustive list, but it should get us started:
'Abdu'l-Bahá: A title referring to the eldest son of Bahá’u’lláh, Abbás Effendi, (1844-1921). He was designated by Bahá'u'lláh as the authorized Interpreter of His Writings. Other titles include The Master, Center of the Covenant, and Most Mighty Branch, but He preferred to be called only ‘Abdu’l-Bahá, the Servant of Glory (referring to Bahá'u'lláh).
Ablutions: A ritual washing of hands and face in preparation for prayers.
Administrative Order: Because the Bahá’í Faith has no clergy, its affairs are administered by a system of elected and appointed institutions. Bahá’ís regard this administrative system as divine in origin because it was created by Bahá'u'lláh, explained and fleshed out by 'Abdu'l-Bahá, implemented by Shoghi Effendi and currently guided by the Universal House of Justice.
Arc: The layout on Mount of Carmel in Haifa, Israel, of the international administrative buildings of the Bahá'í Faith. Presently, these include the Seat of the Universal House of Justice, the International Teaching Center, the International Archives Building, The Center for the Study of the Sacred Texts, and one yet to be built: the International Bahá’í Library.
Auxilliary Board: Part of the appointed administrative bodies, also known as the Institution of the Learned, created by the Universal House of Justice to assist the functions of the Hands of the Cause of God. Members are chosen on the basis of spiritual knowledge and primarily act as advisors to elected institutions and individuals in their geographic areas.
Ayyám’i’Há:Those four days (five in leap year) left over in a solar calendar of 19 months of 19 days each, which occur between the 18th and 19th month, immediately before the period of fasting. Also known as the Intercalary days, they fall in the Gregorian calendar February 25-March 1. This is a festive period Bahá’ís often celebrate with gift giving and hospitality, charity and service to others.
Báb, The: A title meaning The Gate, referring to Hájí Siyyid Mírzá Alí Muhammad Shirazi, (1819-1850) Prophet-Founder of the Bábí Faith and considered by Bahá’ís as the Herald of their faith.
Bahá'í Calendar (Badí Calendar): A solar calendar created by the Báb and used by Bahá'ís, consisting of 19 months of 19 days each, with four intercalary days (five in leap year) inserted between month 18 and 19.
Bahá'í Era: The period from the birth of Bahá'u'lláh until the next Manifestation of God appears, about 1000 years.
Bahá'í World Center: At Mount Carmel in Haifa, Israel. Seat of the Universal House of Justice. It is across the bay from the Shrine of Bahá'u'lláh.
Bahá'u'lláh (Glory of God): A title taken by Mírzá Husayn Alí Nuri (1817-1892) when announcing His Mission. Bahá’ís believe He is the Manifestation of God for this age.
Bahjí: The house near Acre, Israel, where Bahá'u'lláh spent his final years. Bahá’ís consider the shrine where He is buried there to be the holiest sport on Earth.
Consultation: A form of discussion between individuals and within groups by which decisions can be made fairly. It requires avoidance of egotism and unruly passions, frankness and freedom of thought as well as courtesy, openness and wholehearted acquiescence to the majority decision.
Continental Board of Counselors:. Created by the Universal House of Justice to take over the functions of the Hands of the Cause of God, since no more Hands can be appointed.
Covenant: Bahá’ís use this term to mean both an agreement between God and humanity common to all religions that God would send another Manifestation of God in time, and also the specific promise from Bahá'u'lláh prevents schisms from forming in the His faith.
Deepening: Studying the Sacred Writings of the Bahá’í Faith, and those of other religions, as well.
Fast: Bahá'ís fast during the last month of their calendar year. During tht time, adult Believers don’t eat or drink between the hours of sunrise and sunset. Children, the elderly, pregnant and nursing mothers, and the ill are exempt.
Greatest Name: A title of Bahá'u'lláh rendered in calligraphy and often hung in a place of reverence in Bahá’í homes.
Hands of the Cause of God: Members of the Institution of the Learned appointed by Bahá'u'lláh, 'Abdu'l-Bahá and Shoghi Effendi, because of their spiritual understanding and wisdom. They acted as advisors and emissaries to the Believers.
Manifestation of God: The great Prophets of God, those chosen Messengers, who appear in each age, perfect reflections of God’s attributes, and the only way for mankind to know God.
National Spiritual Assembly (NSA): The elected body that deals with the affairs of the Bahá'í Faith at a national level.
Naw-Rúz (New Year): The first day of the Bahá'í calendar, which falls on the vernal equinox, roughly March 20-22.
Obligatory Prayer: A special prayer required by religious law. Bahá'ís can chose one of three obligatory prayers revealed by Bahá'u'lláh .
Pioneer: A Bahá'í who leaves his or her home to live in another country in order to spread Bahá'u'llh's teachings.
Progressive Revelation: The Bahá'í belief that there is only one God Who has sent successive Teachers whose revelations become chapters in one religious Book meant to uplift and educate humanity.
Shoghi Effendi: (1896-1957) Great-grandson of Bahá'u'lláh, appointed by Abdu'l-Bahá in His Will and Testament as the first Guardian of the Bahá'í Faith.
Spiritual Assembly: An elected body that administers the affairs of the Bahá’í Faith on a local level.
Tablet: The term usually given to a letter (epistle) written by The Báb, Bahá'u'lláh, 'Abdu'l-Bahá.
Universal House of Justice: The supreme administrative institution of the Bahá'í Faith. It consists of nine members elected from the body of the Believers of the world, and is seated on Mount Carmel, Haifa, Israel.
Yá Bahá'u'l-Abhá (O Glory of the All Glorious): A form the Greatest Name most often used as an invocation.