(1) Teacher. Gu + Ru = Gu means darkness; and Ru means remover, thus Guru means "remover of the darkness". In the human life a teacher removes darkness of the life, that is why he is called Guru.
(2) Well educated, well skilled in some art or science.
(3) According to Bhavishya Puraan, p 15, Guru is "Who performs Garbhaadhann Sanskaar etc and feeds with Ann, that Braahman is called Guru.
(4) Elder or older people and more educated and learned people are also called Guru. They are not teachers as such, but Guru word is used for them in the sense of older people and more educated and learned people, such as "Guru Jan are around.", means older people and more learned people are around.
(5) Guru also includes, besides above mentioned people, who deserve respect; that is why mother and father are called Mahaa Guru; and husband is called Mahaa Guru of the wife.

A Guru is the person who takes us from darkness to light without any selfish motive or anything in return. The word Guru is a compound of two words, Gu and Ru. Gu means darkness and Ru means light. That which dispels the darkness of ignorance is called Guru. The energy and action for removing darkness are Guru. Guru may always not be a person, it might be a force also driven by grace.

There is an intelligent momentum that pervades the universe that is moving all human beings toward the perfection we call God. Guru is that intelligence. Everyone's receptivity to that intelligence varies. It depends on preparation, which includes the development of Vairaagya or non-attachment, and Abhyaas or practice. In other words, Guru is always there, but the student may not be ready to receive what the Guru has to offer. When the student is prepared, the Guru always arrives to help the student do what is necessary to progress in removing the veil of ignorance. It is said that when the wick and oil are properly prepared, the master lights the lamp.

While we all wait for that master to appear, we are helped by teachers. What we refer to in common parlance is a spiritual teacher/guide. This is the best way to recognize a good teacher: "The teacher who can sit still for a long time is a good teacher because he has practiced something. Listen to him. If the teacher changes his posture many times in five minutes, do not waste your time there."

A true Guru is one who is well-established in the supreme Consciousness. He must be himself "illumined"; otherwise he will be like a blind man leading the blind (Andhena eva Niyamaan Yathaa Andhah), as the Kathopanishad puts it. To guide and instruct a deluded soul and help him to unwind himself and unravel the knotty traits in him, one must have something more than a perfect experience. The Guru must, no doubt, have had full realization but he must also have a complete grasp of the great scriptures. Without the study of the scriptures even the Self-realized masters will not have the language or the technique of expression to convey his profound knowledge to his disciples.

Apart from spiritual knowledge and erudition, the Guru must also have great self-control and the immense riches of a well-developed heart. He must have an irresistible flow of mercy which demands no special cause for its manifestation, especially when it descends upon those who have surrendered themselves to him, having reached his feet as spiritual refugees.

In Kaulak tradition, there are six kinds of Guru -
(1) Prerak - the impeller who instills interest in initiation into Kaulaa tradition;
(2) Soochak - the indicator, who points to Saadhanaa as the means to liberation;
(3) Vaachak - the speaker, who explains the tenets of Kaulaa Dharm;
(4) Darshak - the demonstrator, who by his example shows the performance of rites and rituals;
(5) Shikshak - the instructor, who gives instructions in Saadhanaa; and
(6) Bodhak - Spiritual teacher who enlightens the pupil on spiritual knowledge. The Bodhak plays the central role because his teachings form the nucleus to the contributions made by other teachers; thus spiritual knowledge facilitated by ancillary methods of impelling, indicating, showing, and instructing attains fruition.

One has to pick and choose a Guru; one may end up like a bee that goes from flower to flower accumulating honey; this search for a good guru actually helps a Saadhak achieve wider knowledge. If the Guru-Shishya relationship is agreeable to both the Guru and the Saadhak, they should act in each other's interest: the Guru takes care of the spiritual needs of the Saadhak and the Saadhak treats the Guru like god on earth.

Disqualifications of Guru:
Hinsaa (injury), sinning, bad reputation, devious mind, cruelty (Kroor), selling gold, thieving, plagued with troubles and worries, bad character, adulterous, foul language, sensuous. deceiver. A-Dhaarmik, talkative, greedy, miser, liar, hyperactive, lacks reverence, devoid of Aachaar, many blemishes, money-minded, Consumption (TB), skin disease, diseased nails, diseased teeth, deafness, cataract, bald, lame, deformed, extra body parts conjunctivitis halitosis, large testicles, hunchback, leper, impotent, breaks Kaula practices, loudmouth, pure ritualist, physician, arrogant, vanity addiction wicked, bad company, unbeliever, timid, ignorant of Mantras, epicurean astrologe, usurps property from pupil, wastes Shishya's money, harms out of greed.

Qualifications of Guru:
Knowledge of Veer Knowledge of Divya Knowledge of Kaulaa Knowledge of Sattwa Knowledge of Rajas, Knowledge of Tamas, Knowledge of Mantra, Knowledge of Guru, Knowledge of Devtaa, Meaning of Mantra, Awakening of Mantra, Yoni Mudra, Calm, Self-control, Pure mind, Siddh (perfection) reveals to Shishya previously unknown knowledge reveals spiritual Truths.

There are three classes of Gurus:
(1) Prabhu = Lord;
(2) Vibhu = The Greatest, The Supreme Lord, Omnipresent;
(3) Swaayambhu = self-created, self-existent.
All have equal weight with God.

Sadguru

Who is Sadguru? Sadguru is he who enjoys teaching and therefore teaches for self satisfaction, thanking God to give him an opportunity to teach a good student, and if necessary even without expectation of returns, monetary or otherwise, and does not teach to somehow just to complete a routine duty.

Although Dronaachaarya taught Dhrishtdyumn, knowing it fully well, that he was born from a Yagya  to avenge his defeat and insult by killing Drone through him; but still he may not be called a Sadguru because of some shortcomings, such as (1) his invested interested in Arjun to declare him as the best archer; (2) and due to this to behave harshly with Eklavya  by asking his left thumb in Guru Dakshinaa.

Ideal Sadguru may be (1) Lord Dattaatreya - incarnation of all three super gods - Brahmaa, Vishnu and Mahaadev, (2) Ved Vyaas Jee - incarnation of Vishnu, (3) Saandeepani Muni - Krishn's teacher; (4) Vashishth - Raam's Guru, etc.

How the Guru Are Found?

If you are not able to find out first or second-class type of Guru, you can follow the teachings contained in the books written by realized saints like Shankaraacharya, Dattaatreya and others. You can keep a photo of such a realized Guru, if available, and worship the same with faith and devotion. Gradually you will get inspiration, and the Guru may appear in a dream and initiate and inspire you at the proper time. For a sincere Saadhak, help comes in a mysterious manner.

Mysterious Help From the Lord
Just see how the Lord has helped the devotees in the following instances.
--Ekanaath heard an Aakaash Vaanee, a voice from the sky. It said, "See Janaardan Pant at Dev Giri. He will put you in the proper path and guide you." He acted accordingly and found his Guru.
--Tukaaraam received his Mantra "Raam Krishn Hari" in his dream. He repeated this Mantra and had Darshan of Lord Krishn.
--Krishn directed Naamadev to get his higher initiation from a Sanyaasee at Mallikaarjun.
--Queen Chudalai assumed the form of Kumbh Muni, appeared before her husband Shikhidhwaj in the forest, and initiated him into the mysteries of Kaivalya.
--Madhuraa Kavi saw a light in the firmament for three days consecutively. It guided him and took him to his Guru Nammalvar who was sitting in his Samaadhi underneath a tamarind tree near Tinnevelly.
--Bilvamangal was very much attracted to Chintaamani, the dancing woman. The latter became his Guru.
--Tulasee Daas received instructions from an invisible being to see Hanumaan and, through Hanumaan, to get Darshan of Raam.

Competent disciples are never in want of a competent Guru. Realized souls are not rare. Ordinary ignorant-minded persons cannot easily recognize them. Only a few persons, who are pure and embodiments of all virtuous qualities, can understand realized souls, and they alone will be benefited in their company. So long as there is a world, there are Guru and Ved to guide the struggling souls in the path of Self-realization. The number of realized souls may be less in the Iron Age when compared with the Sat Yug, but they are always present to help the aspirants. Let each man take the path according to his capacity, temperament and understanding. His Sadguru will meet him along that path.

Guru Disciple Tradition
Some very well known Guru disciples' names are given here, starting with Bhagavaan Himself. The beauty of this relationshhip among these people was surprisingly was not based on mere exhibition of funny miracles --