被放到牆上的那個人
目光從那張紙移到紙上的人身上：被大家釘在牆上看的，慢慢變成「那個人」本身。
noun · B2
A person who appears in pin-up pictures, or a person that a certain group of people find very attractive.
海報偶像
核心畫面
Think of a page pulled out of a magazine and pinned to a wall, so that anyone walking past can stop and look at it. Everything this word does starts from that wall.
可以想成一張從雜誌中間撕下來的紙，被釘在牆上，經過的人都會停下來看一眼。這個字的每個意思，都可以從那面牆開始想。
From the word’s history
Wiktionary records pin-up as a deverbal from the phrasal verb pin up, because the photograph was often cut out of a magazine and pinned up on a wall.
來源資料說 pin-up 是從動詞片語 pin up 直接變成的名詞，因為這種照片常常被從雜誌裡剪下來、釘到牆上；做這個動作的名字，後來就變成了那張照片的名字。
Wiktionary entry for pin-up (kaikki extract, source_ref kaikki:3f6f69a190036ae4:1480617293:10268)
From the picture
Also in this word
noun · B2
A picture of a good-looking person, often wearing very little, that is made to be put up on a wall and looked at. It usually comes out of a magazine, and people pin or tape it up in a bedroom, a locker, or a workshop.
美人海報