区别(qū bié) - difference, distinction, to distinguish in Mandarin

区别 (qū bié) is the difference between two things and also the act of telling them apart. As a noun it takes 有 and 没有: 有区别 there is a difference, 没什么区别 there is no real difference. The single most useful frame in the language for a learner is 有什么区别, which is how you ask a native speaker why two near synonyms are not the same word.

As a verb it means to distinguish or discriminate between, usually in a slightly formal register: 区别对待 is to treat two groups differently, and 区别真假 is to tell the genuine from the fake.

The trap is confusing it with 差别 and 不同. 不同 is an adjective, so 这两个不同 works but 这两个区别 does not. 差别 leans towards a gap or disparity in degree, especially a gap you might object to, while 区别 is the neutral word for a distinction of kind. When in doubt over which word applies, 区别 is the safer choice.