There are many definitions of moral relativism.  Most broadly, it means that people make moral judgments based on some individual, cultural, institutional or religious preference.  Sometimes it means that we create moral answers through some decision-making process such as debate or rational reflection.  These definitions imply that moral judgments and values can change over time and that they may differ between people.  There is some overlap with philosophical positions called "pragmatism," "humanism," and so on.

The opposite of relativism would be to say that moral truths "just are":  they transcend humanity, and we can discover them but not change them.  This is often called "moral absolutism."

See www.moralrelativism.com for more information.