distinction; telling apart
The ability or act of distinguishing between similar things. Often used in phrases like 見分けがつく (can tell apart) and 見分けがつかない (cannot tell apart).
この双子は見分けがつかない。
I can't tell these twins apart.
Please tell me how to distinguish the real thing from the fake.
Please teach me how to tell the real one from the fake.
It's hard to tell identical twins apart.