someone who lives by the Guru's teaching

One who follows Gurbani; Guru Oriented; it also means the Bani uttered by the Guru’s mouth.

One who is devoted to God.

Someone who has become God oriented and God filled instead of self centred (manmukh).

One who follows the teachings of Guru Sahib instead of being induced by one's passions.One who lives his life according to the teachings of Guru Sahib.

Gurmukh literally means To face the Guru. The word in Punjabi means to follow the "ways of the Guru" and not to follow your animal instincts and basic desires of the mind. The opposite of Gurmukh is Manmukh, which means a person who follows his own uncontrolled mind or wild desires.