Gurmukh and manmukh are the paired terms in which Sikh scripture describes the two fundamental orientations available to a person. A gurmukh is one whose face is turned toward the Guru, who lives by the Guru's word, whose ego has been dissolved, and who acts within hukam. A manmukh is one whose face is turned toward their own mind, man, self-willed, driven by haumai and by the five thieves of lust, anger, greed, attachment and pride.
The terms occur constantly in the Guru Granth Sahib, very often in the same verse as a contrast, and they carry much of the scripture's moral teaching. What they describe is not two classes of people but two directions, and the tradition treats the manmukh condition as the ordinary human default and the gurmukh condition as something arrived at through the Name, through grace, and through the company of the devout, the sadh sangat.
The distinction is deliberately not a social one, and the scripture is insistent on this. Being a gurmukh has nothing to do with caste, birth, gender, ritual status or outward observance; the Guru Granth Sahib repeatedly criticises those who carry the marks of piety and none of its substance, and the compositions of Kabir and the other saints included in the scripture press exactly the same point in their own idiom. Nor is it a claim about membership, the terms describe orientation, and Sikh commentary holds that a person may be formally initiated and still manmukh.
The content of the contrast is behavioural rather than doctrinal. The gurmukh is described as truthful, content, compassionate, engaged in honest work and in sharing, and free of the appetite for recognition. The manmukh is described as restless, acquisitive, quarrelsome, and doing right things for the sake of appearances. The scripture's interest is consistently in that practical difference rather than in the metaphysics of how the change occurs, though grace is uniformly named as its source, and the tradition denies that a person turns themselves around by their own effort.