The term Lord has several meanings in astrology, and is often used synonymously with the word ruler. Most commonly it indicates the planet that rules the sign on a house cusp. In this capacity, the lord of a particular house has considerable influence over the affairs of that house, according to its own house placement and aspects.
When a house is untenanted or unoccupied by any planets, the lord of a house becomes especially useful in understanding how that house functions. However, the lords of a person's sun, moon, and ascendant houses also exert considerable influence in how they operate.
Lords are sometimes called "accidental house cusp rulers". The term "accidental" means by virtue of the circumstances of a particular horoscope, rather than by virtue of the planet having a special natural or "essential" affinity for the house. The lord of the first house is sometimes called the chart ruler in modern astrology. It should be an important planet in the person's basic orientation to life.
Example: Mother Teresa
Mother Teresa was a nun who ran a hospital for the ill and dying poor of Calcutta, India. The lord of her tenth house of vocation is Venus, located in the traditional eighth house of death. The sun, lord of her eighth house, is also located in the eighth. Jupiter, lord of her first house (chart ruler) conjuncts her Medium Coeli. The lord of her moon's house is also in the eighth.
- Karen Hamaker-Zondag, 1994, The House Connection: How to Read the Houses in an Astrological Chart, Samuel Weiser, Inc.
- Alan Oken, 2008, Rulers of the Horoscope: Finding Your Way Through the Labyrinth, Ibis Press