AFCI (Arc Fault Circuit Interrupter) is a circuit breaker designed to prevent fires by shuting off a power quickly if arcing develops. An AFCI can distinguish between a harmless arc that occurs in switches, plugs and brushed motors and an undesirable arc that can occur from a cut or worn cord or a loose connection in a junction box or receptacle. This undesirable arcing can occur without tripping the regular breaker potentially cause a fire.
The difference between AFCIs and GFCIs is that AFCIs are intended to reduce the likelihood of fire caused by electrical arcing faults; whereas, GFCIs are intended to reduce the likelihood of electric shock hazard. Don't underestimate the importance of the GFCI, they are still needed and save a lot of lives.