Part of the difficulty in defining the term is that it is so subjective. To one person, sex toys might be kinky, while to another, the use of toys might be routine.
Anything not kinky is said to be vanilla.
More About Kink
At one time kink and kinky sex was deemed to be inappropriate, and the vast majority of people would not even talk about it. Talking about kinky acts was sometimes enough to make even the burliest of men blush. Today, however, things have changed. Kink is not only becoming acceptable, but it is also becoming a form of niche entertainment. Although the release of E. L. James' "50 Shades of Grey" has sparked a new interest in kink, the number of books and movies centering around the subject have been on the rise in the past few decades.