The opposite or the rejection of humanism. In a very broad sense, humanism is the acceptance of the values and dignity of human beings; in a more limited sense, it refers to a cultural and intellectual movement that began in the Renaissance (if not earlier) and resurrected in specific human images.
Consciousness, autonomy (understood in principle in the negative sense of freedom from the tension of tradition and the will of tyrants), individuality, and control over nature are among the most obvious features of these images. This view of humanity has been opposed by another view for various reasons, not least because the former seeks to be a universally valid portrait that serves all people equally well (regardless of class, gender, ethnicity, etc.), in fact, it is seriously distorted by contradictory ideological positions.
Antihumanism, of course, is a rejection (without any reason) of this view of humanity). It can be found, for example, in Michel Foucault’s The Order of Things (Les Mots et Les Choses).
If we look through the illusory nature of humanistic concepts of consciousness, freedom, individuality, mastery, etc., we are doomed to see “the death of man as he was defined and defended especially in the post-medieval era of Western culture.
The death of God, proclaimed by Friedrich Nietzsche, proved to be a prelude to the death of the human. At least that is Foucault’s antihumanist conclusion in The Order of Things (1966 [1973], 384ff).