What is racism?
Racism is defined in many ways by many people. Some say racism is about power, when one racial group has more power than another. Some say it is about injustice, when one racial group receives special treatment as compared to another. Some say it is about attitude, when individuals in one group regard themselves as superior. Some say it is about perspective, when people from one group do not understand people from another.
These are all wrong (or at least incomplete).
Racism is simply this: using appearance to segregate people into blocs.
Whenever it is assumed that people have common interests, common experience, common goals, common attributes, common attitudes, common problems–common anything–based merely on their bodily appearance, that is racism. It is always harmful, no matter what is being assumed, and no matter who is doing it.