Gacaca means grass. These are local-level courts that were traditionally used by village communities who would gather on a patch of grass to resolve conflicts, usually between families, employing the heads of each household as judges.
In an effort to speed up the process of justice in the post-genocide scenario, Rwandans have chosen the Gacaca system. The courts often hand out reduced sentences to those who confess to their crimes. Since the process often takes place in the presence of the victims, it can also be a sort of reconciliation and healing for both parties.
Though the system is said to be far from perfect, it is preferred to a conventional system where those in prison could have to wait for years and years without a trial before their case comes up for hearing. Over 1,000,000 people accused of genocide are being held in Rwanda's prisons.