Based on reading from prema-bhakti chandrika, discussion with Damodar Dasji and confirmation by our beloved Babaji Guru word is very widely used. We use this word for anyone. Our school teacher, coach, physical instructor and even sometimes for person who is clever and cunning. It is important to understand what exactly is the meaning of the word Guru or what is this tattva or element which we term as Guru.In general the potency or power to teach others is present in everyone. It is sarva-vyapi. Thus in generic term every living entity is guru. Just as paramatma is present in everyone similarly the guru-tattva is present in everyone. Thus we can even learn from
animals, from trees. Lets understand what is source of this guru-tattva which contains 
guru-shakti. In order to free the conditioned souls, that are grasped by ignorance and falsehood and who are eternally suffering the fire of the three material pangs and are bounded by shackles of sensual attachments, the Lord, who is full of compassion and filled with boundless, causeless mercy, assumes the form of Samasti guru. This Samasti guru is the direct incarnation of Lord and is eternally present in His eternal abode. From this most compassionate and merciful samasti guru, the guru-tattva emanates. Hence the guru- tattva is present in this world in sarva-vyapi form. Also there are great souls in this world, who are devotees completely absorbed in bhajan 24 hours a day, to whom this great guru-shakti from samasti-guru is transmitted. These individual siddha purusas are direct representative of samasti-guru in this world and are called Vyasti-guru. Thus there are many individuals who carries the guru-shakti whose source is direct incarnation of Lord, samasti-guru. Thus many times it is said Guru in one. That refers to Samasti-guru. The same samasti guru is present in this world as various individuals in form of Vyasti-guru. Thus guru and Lord are non-different in that term. Infact Vyasti-guru is greater than Lord because we can easily serve Guru (vyasti) and directly talk to him, serve him, take instruction from him in this material world, but only very very rare personalities can get audience of Lord Himself.
Thus samasti-guru is present in all vyasti gurus in this world to rescue the people of the world from the grip of maya and give them devotion to the Lord. They can take them to lotus feet of Sri Bhagwan Himself.Now one may ask, that I also have guru-tattva so I am also vyasti-guru. No. I also have guru-tattva so I can also tell people to chant,hear and tell the glories of Lord. But I am not siddha yet, I am not a great soul, I am not myself sitting at lotus feet of Lord. Thus I cannot be Vyasti-guru. Only those personalities who have attained the lotus feet of Lord and are constantly engaged in His service are direct expansions of the Lord in form of Real Guru (Vyasti). What happens if I consider someone siddha purusa and think him to be real Guru but actually he is not?
The guru-tattva works based on individual nistha. Since guru-tattva is emanating from the Supreme Lord Himself, it will work irrespective of individual. Thus if someone chooses incapable person as guru, the guru-tattva will still work but it won’t take one to lotus feet of Lord, however, it will take him to the real guru (vyasti-guru) who will help the devotee in getting service to lotus feet of Lord.The purport is that only Vyasti-guru can act as real medium to achieve Lord. He is only the one who can give diksha to devotee. If someone else who is not siddha gives diksha (the adhikar not given to him by Lord and his guru) still the devotee who gets diksa (so called) can progress on spiritual path because of his nistha and guru-tattva principle and in the end he will get his real guru.
– NitaiCharan Das
Charan Pahari 