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.
From the word’s history
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, "meh" (etymology 1)
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