These stats represent the percentage of searches which result in one or more clicks vs the percentage of searches that don’t lead to any clicks at all.
Let’s take a closer look at the keyword “chauffeur” as an example. Its search volume is 66K and its clicks count is 13K. One may be confused, because 13K doesn't make 18% of 66K.
The thing is, those clicks are not distributed within searches equally. 85% of the searches didn’t result in any clicks at all, while 15% of them resulted in some clicks (not necessarily one, it can be 2, 3 and more per search). When summed up, they will make 11K clicks in total.