Kinky sex is any form of sexual activity that cannot be described as vanilla sex.
Although in the popular mind, kinky sex must involve kinky, bizarre and unusual acts, it may be no more than playfulness, rather than any form of perversion. What is considered kinky is highly subjective, but may include BDSM, role play, sex toys, exhibitionism, fetish and more.
Not all kink is necessarily kinky sex. While there is always a sexual element, intercourse is not necessarily required. For example, a dominatrix will rarely have sex with her slave, but the power exchange is clearly kinky.