Question: "What is metaethics?"
Answer: There are three main divisions in the philosophy of ethics. Applied ethics is the most practical—it identifies wrong and right actions in various fields of human interest. Normative ethics doesn't speak to specific actions, but it does try to develop a working framework by which actions can be deemed ethical or unethical. Metaethics is the study of ethics itself. It delves into the language, nature, motivation, and source of morality.
The two main schools of metaethics are cognitivism and non-cognitivism. Cognitivism studies the language of ethics. A statement that describes a moral characteristic (“war is bad”) has the same sentence structure as a statement about an object's physical characteristics (“trees are leafy”). Cognitivism claims that this similarity is valid, because moral statements do describe moral conditions of things (although the judgment expressed in the statement may be wrong—war may not be bad, trees may have lost their leaves). Non-cognitivism insists that moral statements cannot describe true characteristics, because morality isn't real. There is no moral truth to which language can refer. So, however much like a physical description it may resemble, a moral statement can only express emotion, preference, or some other subjective viewpoint.
Cognitivism has further divisions. Given that language can describe real moral qualities (even if those qualities are in error), what is the nature of morality? Is it objective or subjective? Moral realism asserts that morality is real and objective. Moral statements are not based on opinion, and they either can be reduced to a simple fact about the natural world or are given to us by a supernatural being or force. Anti-realism rejects this theory, saying that morality is mind-dependent—it is given value by the choice of a mind. That mind may be an individual, as in individual subjectivism; an entire society, as in cultural relativism; or God, as in Divine Command Theory.
Non-cognitivism also gives several options. If moral statements do not communicate a real quality of an action, then what are they? Emotivism says they are emotions or preferences. Prescriptivism says they are subtle commands, expressing what the speaker wishes to happen in regard to a situation. Norm-expressivism is like emotivism but insists moral statements represent the feelings of a community. And quasi-realism teaches that, although moral statements do not express any real quality, it's best that we pretend they do.
There are many other arguments in metaethics. What drives someone to act ethically in the first place? Are complex ethical qualities like courage as useful as basic qualities like goodness? And how much of reality can our limited intellects really understand? At what point does the desire for hard evidence give way to "it seems right"?
The Bible is actually very specific about the metaethical use of language. In Genesis 1 God spoke, and His words became reality—not wish or preference or hope, but hard rock and fuzzy badgers. And we are not called to wish, we are called to speak truth (Proverbs 12:17; Zechariah 8:16). God created language to express fact.
Of course, the Bible is equally adamant that morality is objective. Second Kings 17:37 and Matthew 5:17-18 speak to the permanence of ethics. God gives the law (Exodus 20:1). Our thoughts are too limited to discern or create ethical concepts (Isaiah 55:9). Our ways only lead to death (Proverbs 14:12). We cannot fully know what is right by inferring ethics from nature or intuition; we need the Word of God (2 Timothy 3:16-17).
Using human intellect alone to try to determine the nature of language and truth and morality is futile. As Ecclesiastes 12:12-14 says, "…the writing of many books is endless, and excessive devotion to books is wearying to the body. The conclusion, when all has been heard, is: fear God and keep His commandments, because this applies to every person. For God will bring every act to judgment, everything which is hidden, whether it is good or evil."