The Sanskrit word “guru” means spiritual teacher; however it is also often used to refer to teachers of all kinds—whether it’s teachers of music, Ayurvedic medicine, cooking, etc.
“Guru” as an adjective means “heavy or weighty” as in “one who is heavy with spiritual knowledge and wisdom.” Additionally, “guru” means servant; “guru” does not mean master.
On the spiritual platform, the word “guru” refers to a state of heart and mind, rather than a particular position or post. As we are all spirit souls, eternal parts and parcels of God, the essence of the yoga teachings is that each of us should become guru - one who is self-realized and living a life of bhakti: loving service to God and all living beings.
The great Vedic/yogic scripture Chaitanya Charitamrita states, “By My command, be guru and save the people from their suffering.”
It’s very important to understand that actual gurus never see themselves as the dominator or master of anyone. They never teach that they have become God, or realized they are God, or try in any way to take the place of God in people’s lives. In fact the exact opposite is true: the guru knows only God can truly make a person happy and that God will guide a person and relate to them from within their heart, giving them the love and satisfaction that will truly fulfill them. So guru is one who is always teaching people to turn to God within themselves and take shelter of Him.
A guru is someone who is so filled with bhakti or love for the Supreme or Original Cause—and therefore love or compassion for all living beings, who are part and parcel of the Original Cause—that they see themselves as the servant of everyone, dedicating their lives to helping every living being find true happiness.