There are many differences between the two types of ethical relativism. First of all there is the individual ethical relativism. Individual ethical relativism is an ethical judgment and also includes beliefs. This is an expression that uses moral outlooks and the attitudes of individuals. An easy way to say it is people have their ethical views and other people have their own ethical views, too; neither is right or wrong. An example of this is some parents believe in spanking there children for a punishment and other parents don't think it's necessary, but you can't judge the way on how a parent or both parents raise their children.
Then there is social or cultural relativism. Social or cultural relativism is an ethical view that varies from society to society. It is based on the basis for moral judgments lying in social or cultural views. The easiest way to describe this is people should act the way the norms of society think you should act.
No society is the same so expect different things all the time. In Holland people put mayonnaise on there French fries and in America people use ketchup, people may think that is weird, but it is a norm of their kind of society. Different cultures all over the world do different things everyday; because that is the way they were brought up in their society.
So what is the difference? Individual ethical relativism is one persons view vs. another persons view but neither is right or wrong. Social or cultural relativism is one cultures view vs. another cultures view and neither is right or wrong, too. There is no right or wrong answers on how societies deal with life.