In Sikh Dharma, the below terms are defined in the following way:

Gur: The formula which makes the difficult easy.

Guru: That force which dispels the darkness of ignorance (‘gu’), and brings the light of divine understanding (‘ru’). It is the application of the formula (Gur) to make our life excellently balanced and successful.

Satguru (True Guru): The one who shows us the truth and gives us the power to be excellent.

Sri Guru (Greatest Guru): Gives us universality, experience, and command of the radiant and subtle bodies, which gives us the essence of the infinite.

Wahe Guru (Wow! Guru): The Guru that is beyond words to express. The words “Wahe Guru” are the mantra Guru Gobind Singh gave at the first Amrit ceremony, and it is the first mantra of the Sikhs. It is the mantra of the “Tresha Guru” or three in one: first is Brahma – creator of the universe; Vishnu – the sustainer, and Shiva   lord of deliverance or destruction. This mantra is the personal identity of God. It gives us excellence and protection in our human life.

~This information was originally shared in the book Living Reality (1994) by Bibiji Inderjit Kaur Khalsa.