Picture a narrow line of light travelling steadily across something, from one edge to the other, missing nothing. It is not looking at the whole thing at once; it is going over it in strips and reading as it goes. Whatever it passes over gets turned into information a computer can hold. Every meaning of scanner is a machine doing that, and what changes between them is only what is being swept: a page, a body, a small printed code, or a long row of radio frequencies.
From the word’s history
The word is scan plus -er, the ending that names the person or thing that does something, as in print and printer. So a scanner is simply the thing that scans.
這個字是 scan 加上 -er。-er 在英文裡用來指「做這件事的人或東西」，像 print 變成 printer。所以 scanner 就是「負責掃的那一個」。這也說明為什麼從辦公室的機器到醫院的儀器，全都能共用同一個字。
Wiktionary entry for scanner, etymology supplied in packet (kaikki:3f6f69a190036ae4:384154926): From scan + -er.
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