Searching for stock risk measure where a value of around 15 is fine

I am reading through some stock analysis documents (unfortunately they don’t seem to be available online). They calculate something that they call "risk". For Amazon stocks its around 18 (maybe percent?) for the past 10 years.
For other (valuable/emerging) companies it’s also between 10 and 25 in the period of the past 10 years.

Unfortunatelly they do not clearly define how the risk value is calculate. It seems like the chance of losing money (when bought at any day within the 10 year period and sold anytime later – whats the chance of losing money?) and the average loss is somehow used.
Does anybody have an idea what risk measure this could be?
The measures that I know/researched are usually around 1 or 100.

Sidenote:
For Amazon I also calculated:

• Chance of winning money (when buying in the last 10 years and selling at some arbitrary day later): ~96% (3,022,635 cases)
• Therefore chance of losing money: ~4% (143,751 cases)
• Sum of profits (winning case): 2,720,441,950 USD
• Sum of Loses (losing case): -8,653,463 USD
• Therefore average loss: -8,653,463/143,751 = 60.2
  I don’t see a way to get value 18 out of that data…