身體真的轉半圈
這一族就是核心畫面本身，轉的是人和板子。
noun · B2
A turn of half a circle, so that you finish facing the way you came from. It is used about tricks and moves on a skateboard, a bike, a snowboard, or off a diving board.
轉半圈（動作）
核心畫面
Stand still and turn until you are looking straight back the way you came. That is half a circle, 180 degrees, and the number alone is enough to name it. Everything else this word does keeps that half-turn and changes only what is turning: a board, a plan, or two things already sitting at opposite ends.
可以想成一個人站著，轉到正對著剛才來的方向。那就是半圈，180 度。英文只留下這個角度，就足以指出整個動作。其他用法…更多收起
可以想成一個人站著，轉到正對著剛才來的方向。那就是半圈，180 度。英文只留下這個角度，就足以指出整個動作。其他用法都沿用這個半圈的畫面，只是換掉轉的東西：有時候是滑板，有時候是想法，有時候只是兩個剛好在兩端的東西。From the word’s history
Wiktionary gives the origin plainly: the noun is shortened from '180-degree turn'.
Wiktionary 直接寫著它來自 180-degree turn（一百八十度轉身），說話時只留下角度這個數字。
Wiktionary (kaikki dump, source_ref kaikki:3f6f69a190036ae4:1443795091:5368), supplied in the evidence packet
Two branches
轉的是想法或立場
把轉半圈的身體換成一個人的立場。原本朝這邊，轉完朝那邊，中間沒有留下一點舊主張。
noun · B2
A complete change in what someone thinks, wants, or plans, so that they end up at the opposite of where they started. It is almost always used with the verb do: do a 180.
完全改變主意
原始詞典資料3 筆記錄
以下是外部詞典記錄的用法，原文照列，我們還沒有寫成教學內容。上面的說明才是我們自己寫的；有些用法可能上面已經講過了。
180noun
- 1
hobbieslifestylesportsAn instance of spinning 180 degrees, so that one is facing in the opposite direction.
- He did a 180 off the diving board.
- 2
The exact opposite.
- The friendly welcome was a 180 from what she had been expecting.
- As a result of his refusal, the employee was subsequently canned in 2015 on the basis of […] being boring […] In other words, it was a complete 180 from most employees who get fired for being too wild.
- 3
A complete change of direction or opinion.
- She used to like turnips, but she did a 180 and now hates them.
- Got so sick of crying, so just lately / When I catch myself, I do a 180
資料來源：英文維基詞典 English Wiktionary（CC BY-SA 4.0）。 原文照列，未經改寫。