Scan

The verb 'to scan' has several distinct meanings, some of which contradict each other. Be clear about which one is meant when you read them in books from different areas.

• All students now are probably familiar with the idea of 'to scan' as 'to make a photocopy of'.
• If you are learning English, you will often hear teachers talking of scanning a text. They mean 'reading over quickly to get an idea of what the text is about'.
• If you are studying medicine (or are an appropriate patient), you should be familiar with the idea of a scanner as a machine that examines in great detail, with powers to see things that human observation cannot.
• Teachers of literature will usually mean 'to analyze the patterns of' traditional metre in verse.

The history of the word as recorded in OED may be interesting.

The last meaning above is the oldest recorded, from 1398. This came from the Latin scandere, originally 'to climb', but used in later Latin for 'to scan verses'. (That meaning may have developed from the practice of counting metrical feet on the fingers, counting a pentameter by 'climbing' up all the digits of one hand.).

From that application to verse came several meanings recorded as Obs[olete]: 'to judge [the correctness of]', 'to test', 'to criticise', and, the start of one of the contradictions in the use of the word, from 1550, 'to examine in great detail'.

This leads on to OED's sense 6., which diverges from 6. a., first recorded in 1798, "To look at searchingly, examine with the eyes" and, from 1926, 6. b. "To search (literature, a text, a list, etc.) quickly or systematically for particular information or features." It is this sense that gives us the common use in TEFL of 'reading over quickly to get an idea of what the text is about'. 6. a. leads to 6. c., "To cause (an area, object, or image) to be systematically traversed by a beam or detector; to convert (an image) into a linear sequence of signals in this way for purposes of transmission or processing". This is the meaning in medicine, in radar, in photocopying, and in many applications in electronics, such as television, etc.