A shrug with a sound attached. Someone asks how it was, and instead of picking good or bad you let out one flat syllable that means 'it did not move me'. Everything in this group can be held against that: the sound itself, the same flatness used to describe a thing, the same flatness used to describe how you feel, and finally the shrug treated as a thing that a film or a plan can receive.
Wiktionary records meh as possibly from Yiddish מע (me, 'so-so'), first attested in 1928 with interjection use dated to 1992, and popularised by the American cartoon The Simpsons, which used it in a 1994 episode.
維基詞典記的是：meh 可能來自意第緒語的 מע（大概是「普普」），1928 年就有紀錄，當感嘆詞用則從 1992 年起算，後來因為美國動畫《辛普森家庭》1994 年的一集而傳開。這條線索跟核心畫面一致：它一開始就是一個聲音，不是一個有部件的字。
Wiktionary entry meh, etymology 1 (packet source_ref kaikki:3f6f69a190036ae4:723575195)
Two branches
那一聲：不置可否的回應
這個家族就是核心畫面本身：先是發出來的那一聲，再來是把那一聲當成一個可以「收到」的東西。中間沒有轉義，只是同一個聳肩換了語法身分。
interjection · B1
Said on its own, usually as a whole answer, to show that you do not care much about something or were not impressed by it. It means something close to 'it was okay, and that is all'.
還好啦／沒什麼感覺
形容詞：東西普普，人也提不起勁
同一個平平的感覺，從「回答」搬到「形容」。指著東西說，就是這東西沒什麼看頭；指著自己說，就是心裡沒有力道。兩個方向共用一個畫面，只是箭頭朝外還是朝內。
adjective · B2
Not very good: ordinary, flat, and not worth getting excited about. It says a thing was okay but nothing more.
普普的／不怎麼樣