A response format in which the respondent is asked to rate something by marking a point on a line. These are often horizontal 10 cm long lines. The scoring from a paper form is simply the distance along the line.
An article from 1969, Zealley, A. K., & Aitken, R. C. B. (1969). Measurement of mood. Proceedings of the Royal Society of Medicine, 62(10), 993–996. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1810824/ throws a lovely historical light on the use of a VAS to rate mood (there depression) and on how things have changed in the last 50 years.
The simplest VAS tends just to have anchor words (e.g. “fine” and “terrible”) at each end of an otherwise unembroidered line but other versions have numbered marks, typically 0 to 10 while others have words against points on the line between the extremes. Others use emoticons instead of words. We recommend searching for examples: here’s an example search. As ever, our advice is not to be excited by these (some are lovely) and design your own scale (as we say in Chapter 3: “Shall I just invent my own measure? Stop! Don’t do it! Don’t jump!”)
Chapter 3 and, a bit, Chapter 4.