Satgur or Sat-Guru consists to 2 roots - Sat meaning 'true' and Guru meaning 'spiritual teacher'. So the word means the 'true spiritual teacher'.
Guru is a word which in turn consists to 2 roots - 'Gu' and 'Ru'. So the word Guru means a person who dispels the darkness of ignorance ('gu'), and proclaims enlightenment ('ru'). It is the application of the formula to make our life excellently balanced and successful; to bring vision and spiritual awareness in our minds and to move us away from selfishness and limitedness in our behaviour and in our attitudes.
A Guru is a teacher or enlightener who brings his followers (devotees) from darkness to light. Guru is an idea or an institution, not a person. However, a person can attain this level of clarity of reality. The GURU, is a spiritual guide or preceptor. The term, long used in the Indian religious tradition, has a special connotation in the Sikh system.
The Sikh faith itself signifies discipleship, the word 'Sikh' (sisya in Sanskrit and sissa or sekha in Pali) means pupil or learner. The concept of Guru, the teacher or enlightener who guides his/its devotees (Sikhs), is thus central to Sikhism. The Guru, according to Sikh belief, is the vital link in man’s spiritual progress.