A neutralist is a person who believes their country should stay out of other countries' quarrels and wars — not joining either side, not signing up to a military alliance. It is also used as an adjective: "a neutralist government", "neutralist foreign policy". The word carries a whole political position, not just a mood: neutralists argue that staying out keeps a country safe, keeps it free to trade with everyone, and keeps it able to help both sides talk. Their opponents answer that staying out of a fight between a bully and a victim is really a choice to help the bully. So the word is often used with a slight edge by people who disagree with it. It belongs mostly to writing about politics, history and international affairs — newspapers, textbooks, speeches — and you will meet it most often in accounts of the Cold War, when a number of countries refused to join either the American or the Soviet side. Note the definition you were given describes the state of not taking sides — that is really "neutrality" or "neutralism"; "neutralist" is the person who wants that, or the word describing them. Keep the family straight: neutral (the plain adjective, usable about anything at all), neutrality (the state), neutralism (the policy or belief), neutralist (the believer).

中立主義者；（形容詞）中立主義的