What do SSC mean in kink?

SSC (safe, sane, consensual) is an older phrase. Some people feel it can hide the fact that no activity is completely safe, which is why RACK (risk-aware consensual kink) became popular. Some folks also feel that using the term sane as a defining factor may exclude those that may struggle or have struggled with their mental health in the past, and been labeled 'insane' by a flawed medical system.
A third, PRICK (personal responsibility, informed consent kink), puts the focus on each person's responsibility. None of them is official, and people choose the one that fits how they practice.