From Mahabaratha, Ramayana we find Guru's like Dronacharya, Viswamitra, Sandipani etc.,
It is emphasized many times in Mahabaratha that Guru should be respected well. If a person humiliates/ disrespects his guru, then the person is a sinner.
My doubt is whether any text clearly defines 'GURU'? Does the current teachers in schools/ colleges/ universities are guru's? Does an undeserved person can be a guru? Suppose a person has very much angry behavior, is he eligible to be a guru?
No. They are just teachers but not Gurus as far as how Gurus are understood in Hindu Dharma.
In Vedic Dharma, Guru is one who initiates you into the Vedas by giving you the Gayatri Mantra. This Samskara is called the sacred thread ceremony or the Upanayanam.
Manu Smriti 2.149. (The pupil) must know that that man also who benefits him by (instruction in) the Veda, be it little or much, is called in these (Institutes) his Guru, in consequence of that benefit (conferred by instruction in) the Veda.
And in Tantra, Guru is one who relieves you from the ignorance by initiating you into a Mantra. This process is called the Guru Deeksha or the Mantra Deeksha or the Deeksha Samskara. And the Mantra is called the Guru Mantra.
In Tantra, there are three lines of Gurus : The Divine line (comprised of Gods and Goddesses as Gurus ) , The Enlightened line (comprised of Siddhas or enlightened beings as Gurus ), and the Human line (comprised of human beings as Gurus ).
The Divine line or the Divyauga Guru Pangti consists of 12 Gods like Adi Natha and his consort, Sadashiva and his consort, Iswara and his consort, Rudra and his consort, Vishnu and his consort, etc.
The enlightened line of Gurus or the Siddhauga Pangti comprises of 11 Gurus viz- Sanaka, Sanananda, Sanatana, Sanatkumara, Sanat-Sujata, Dattatreya, Vyasa, Vamadeva etc.
And, the human line of Gurus or the Manavauga Pangti consists of 6 human beings viz- Nrisimha, Mahesha, Bhaskara, Mahendra, Madhava, and Vishnu (not to be confused with Lord Vishnu ).
And the disciples of these 6 human Gurus are all the Hindu Gurus that we have in the current world.
Divyaughe ChAdinAthashcha Tacchshaktischa sadAshivaha| Tathpatni Cheswarastasya BhAryA Rudrascha Tadvaduhu|| Vishnushcha TathpriyA BrahmA TathkanthA DwAdaseritAha|
The Divyauga Guru Pangti consists of 12 Gurus viz- Adinatha, Sadashiva, Iswara, Rudra, Vishnu and Brahma along with their respective shaktis or consorts.
Siddhaughe Sanakaishchaba Sanandashcha SanaAtanah| SanatkumArascha SanathsujAtascha Rhibhukshajah|| DattAtreyo Raibtako VAmadevastathaha Parma| Tato VyAsah Sukaishchava Ekadasha SamiritA||
The enlightened Gurus are 11 in number and they are- Sanaka, Sananda, Sanatana, Sanathkumara, Sanath-Sujath, Rhibhukshaja, Dattatreya, Raivataka, Vamadeva & Vyasa.
MAnvaughe Nrisimhashcha Mahesho BhAskara TathA| Mahendro MAdhavo Vishnu Shadethe Cha PrakirtithAha||
The human lines of Gurus consist of six Gurus namely- Nrisimha, Mahesha, Bhaskara, Mahendra, Madhava & Vishnu.
KulArnava Tantram, Chapter 6, Verses 64-67.
So, the point is, my badminton teacher is only a badminton teacher but not a Guru in the strict Hindu sense of the word unless he duly belongs to any one of the lineages mentioned above. Similarly for your school teachers.
Does an undeserved person can be a guru? Suppose a person has very much angry behavior, is he eligible to be a guru?
No, certainly not. In KulArnava Tantram's 13th chapter we find the descriptions of such long lists of qualities that a Guru or Sath Guru must possess. One such quality is :
Vedako Vodakah Santhah Sarvajivadayaparaha| SwAdhinendriyasamchAra Shadavargavijayakshamaha||
A Guru is one who is capable understanding the hidden truths of Vedas, who is calm, who has compassion for all beings, who has mastered over the movements of his senses, who is capable of winning over the shadavarga or shadaripus (which are anger, lust etc ).
KulArnava Tantram, Chapter 13, Verse 42.
So, needless to say, a very angry person is not fit to be a Guru. Because he is yet to master anger, which is one of the shadaripus.
As you can see from my answer here, that anyone or anything that teaches you something can also be considered as a Guru. Lord Dattatreya had such 24 unconventional Gurus. But whatever i have written above holds if we use the word Guru in the strict and usual Hindu sense.
It is up to the student 'disciple' to take the teacher for a guru. No one can decide it for the student. No one can come between the Guru and Shishya. Just like no one can come between God and the Devotee. It's a relationship of ecstasy, bliss. To be experienced.
Again whether one has one guru or many also depends on the disciple. It is a one way relationship. Everything depends on the disciple. This should be understood. It is one way. The moment you start seeking a guru, the guru starts unfolding. This is profound.
