You're a Soviet artist from the 1920s?
It is also a concept used in the social sciences describing the creation and sharing of intersubjective perceptions of reality, with impressions people have about what is real being passed off as knowledge. This is in contrast to the more common stance of believing knowledge is a solid, objective grasp of fact that can be derived from sensory input and studies of natural phenomena. Very few claims about truth may be proved or disproved beyond all doubt without falling back on faith, however, so far as I can tell.
I'd recommend looking into the works of Ernst von Glaserfeld, in particular, if your curiosity is piqued.
Going back to morality, my position is good and evil do not exist outside the mind. And even then it only exists for us as a side-effect of adaptations in our species such as to nurture offspring, form cohesive bands, rally group members to dispose of troublesome oppressors, etc. giving rise to feelings about what is right or wrong. In most members of our species these impulses appear to provide the framework upon which theories of ethics are constructed as tools for making sense of our subjective moral impulses. Some folks, like sociopaths, do not function in quite the same way and as a result operate within a different set of restraints on desires to advance their own, best perceived interests.
I have very strong opinions about when political violence is and is not justified. But my point is no matter how passionately I feel and to how great of lengths I go to rationalize the merits of those views as being superior to alternatives, they will still amount to nothing more than opinions. You see, moral relativism is not a rejection of moral orders. It is an acknowledgement of people being able to temper feelings with reason and experience to build up shared understandings of what is good and bad for practical purposes. Having to invent moral standards does not make them any less useful.
So when I or someone else takes offense to an armed robbery it is genes and socialization at work - not an indication of insight into principles of inherently beneficial behaviour.