colloquial exclamation meaning "what's that?/what are you talking about?", used to express surprise, disbelief, or mild ridicule
A: 昨日UFOを見たよ。 B: 何それ、冗談でしょ？
A: I saw a UFO yesterday. B: What the—you're joking, right?
彼の言い訳を聞いて、みんな『何それ』と呆れた。
When we heard his excuse everyone was like, "what's that?" and were exasperated.
子供がくっつけてきた発明品を見て、『何それ？』と聞いた。
I asked, "What's that?" when I saw the gadget the child had put together.