Relativism is the idea that
The major categories of relativism vary in their degree of scope and controversy.
"There is nothing either good or bad, but thinking makes it so." -
Hamlet: Act 2, Scene 2.
Philosophical relativism, in contrast, asserts that the truth of a proposition depends on the metaphysical, or theoretical frame, or the instrumental method, or the context in which the proposition is expressed, or on the person, groups, or culture who interpret the proposition. 
Methodological relativism and philosophical relativism can exist independently from one another, but most anthropologists base their methodological relativism on that of the philosophical variety. 
The concept of relativism also has importance both for
Descriptive relativism assumes that certain cultural groups have different modes of thought, standards of reasoning, and so forth, and it is the anthropologist's task to describe, but not to evaluate the validity of these principles and practices of a cultural group. It is possible for an anthropologist in his or her fieldwork to be a descriptive relativist about some things that typically concern the philosopher (e.g., ethical principles) but not about others (e.g., logical principles). However, the descriptive relativist's empirical claims about epistemic principles, moral ideals and the like are often countered by anthropological arguments that such things are universal, and much of the recent literature on these matters is explicitly concerned with the extent of, and evidence for, cultural or moral or linguistic or human universals. 
The fact that the various species of descriptive relativism are empirical claims, may tempt the philosopher to conclude that they are of little philosophical interest, but there are several reasons why this isn't so. First, some philosophers, notably Kant, argue that certain sorts of cognitive differences between human beings (or even all rational beings) are impossible, so such differences could never be found to obtain in fact, an argument that places a priori limits on what empirical inquiry could discover and on what versions of descriptive relativism could be true. Second, claims about actual differences between groups play a central role in some arguments for normative relativism (for example, arguments for normative ethical relativism often begin with claims that different groups in fact have different moral codes or ideals). Finally, the anthropologist's descriptive account of relativism helps to separate the fixed aspects of human nature from those that can vary, and so a descriptive claim that some important aspect of experience or thought does (or does not) vary across groups of human beings tells us something important about human nature and the human condition.
Normative relativism concerns normative or