拖在後面載東西的車
這一組就是核心畫面本身：自己不會動，被拉著，用來載東西。
noun · B1
A vehicle with wheels but no engine of its own, pulled along behind a car, truck or tractor to carry heavy or bulky things.
拖車；拖板車
核心畫面
You can think of trailer as whatever comes along behind, pulled by something else. It has no engine of its own: the car goes, and it follows. Hold that picture and the word opens up — the box of tools behind the truck, the little room you sleep in on the road, the home that was towed in once and never left, and the short reel of film that used to run along behind the main feature.
trailer 可以想成「跟在後面、被拉著走的那個」。它自己沒有引擎。前面的車走，它才走。抓住這個畫面，這個字就打開…更多收起
trailer 可以想成「跟在後面、被拉著走的那個」。它自己沒有引擎。前面的車走，它才走。抓住這個畫面，這個字就打開了：卡車後面那台載工具的、路上睡覺的那間小房間、拖來一次就再也沒走的那個家，還有以前接在正片後面播的那一小段影片。From the word’s history
The source records trailer as trail + -er, the thing that trails. It also explains the film sense directly: previews were once shown after the main feature rather than before it, so they trailed along behind it, and the name stayed when cinemas moved them to the front.
資料把 trailer 記成 trail 加 -er，也就是「跟在後面的那個」。它還直接說明了預告片為什麼叫這個名字：以前預告是放在正片後面播的，等於跟在正片後面跑。後來戲院把它移到片頭，名字卻沒改。
Wiktionary entry for trailer (kaikki:3f6f69a190036ae4:404947959): 'From trail + -er. The film sense derives from the fact that previews were formerly shown after the main feature, rather than before as is usual today, that is trailing after the main feature.'
Three branches
拖著走的、可以住的那一種
一樣是被拉著的那台車，只是裡面裝的不是貨，是人的生活。
noun · B1
A vehicle with beds, seats and a small kitchen inside that you pull behind your car and live in while you are travelling or on holiday. The source marks this use as American English.
露營拖車（美式）
接在正片後面的那一小段
這一組跟核心的連結，資料本身就說得很清楚：它也是跟在後面的那個東西。
noun · B1
A short set of clips taken from a new film, TV show or video game and put together to show people what it is like, so that they will want to watch or play it.
預告片