If something is unusual, it does not happen very often or you do not see it or hear it very often.
They have replanted many areas with rare and unusual plants.
他们在很多地方重新种上了珍稀的植物。
If you describe someone as unusual, you think that they are interesting and different from other people.
He was an unusual man with great business talents.
他不同凡响,具有高超的商业才能。