Updated: DECEMBER 10, 2018
Risk-aware consensual kink (RACK) is a philosophy governing BDSM activities and behaviors. Risk-aware means that all the participants know the risks involved in the activity (BDSM activities are not always risk-free). Consensual means that all the participants have freely consented to the activity, and that no one has been coerced. Kink refers to alternative sexual activities.
More About Risk-Aware Consensual Kink (RACK)
RACK was developed in reaction to another term used to describe BDSM activity: safe, sane and consensual (SSC). These terms are similar, but they differ in that RACK acknowledges that some BDSM activities may not be risk-free (or "safe"), so RACK emphasizes personal responsibility for understanding the risks involved in some BDSM activities and particpants' need to accept those risks in order to participate.
RACK also tends to include a larger variety of activities (for example, blood play would not be considered under SSC but does fall under RACK), and to put the emphasis on the fact that few BDSM activities are actually risk-free.
RACK is mot often used in the BDSM community to refer to edgeplay, while SSC is used to explain BDSM activities to people outside of the BDSM world. In the end, however, the choice of using either SSC or RACK to define your activities depends on your understanding of what is ethically defensible. Both can be used at the same time to define different kinds of activities.