Think of the sound people make when they hum with no words — la la la — and then turn that sound into a place on a map. It is soft, pleasant, and nothing in it is solid. Whatever is said to be in that place has floated away from the hard world: a mind that has stopped listening, a plan that no real numbers support, even a whole city that is felt to be made of film and sunshine.
可以想成有人不知道歌詞、隨口哼出的那串聲音——la la la——然後把那串聲音變成地圖上的一個地方。那裡輕飄飄的，很舒服，沒有一樣東西是硬的。被說成在那個地方的東西，都已經離開了現實：可能是一顆不再聽人講話的腦袋，可能是一個算都算不出來的計畫，甚至可能是一整座城市，被覺得是用陽光和電影做成的。
From the word’s history
Wiktionary records one entry as la (a syllable used in singing) + land, and a second entry as a blend of LA (Los Angeles) with that same dreamland word.
Wiktionary 記了兩條：一條是 la（唱歌時用的音節）加上 land；另一條是把 LA（洛杉磯）跟前面那個幻想之地混成一個字。
Wiktionary, "la-la land"