Generally defined by social justice warriors to mean an entire society that is set up to discriminate against anyone who isn't white. People who believe in this concept believe that anyone who isn't white won't be able to succeed in this world because everything around them has a history and culture associated with it that's designed to keep non-whites down.
In reality, it's an attempt by leftists to create a "no lose" definition in which anyone who disagrees with it is a "racist" and is part of the problem. Additionally, it's designed to ensure that people of color are dependent on white liberals for everything that they obtain or earn in life.
American university professors (who are almost always white) will preach this concept to their students until they're
blue in the face and will threaten to file a bias incident against them if they dare to have a
different opinion.