Three protection types, and they’re easy to confuse - especially since combination breakers exist now. Ground Fault Circuit Interrupter (GFCI) detects current leaking to ground - typically 4-6 mA - and trips in milliseconds. It’s protecting people from electrocution. Arc Fault Circuit Interrupter (AFCI) detects the electrical signature of an arcing fault - the kind that starts fires inside walls where you’ll never see it. Different problem, different solution.
Dual Function Circuit Interrupters (DFCI) do both, and with the 2023 NEC requiring both AFCI and GFCI in many locations simultaneously, dual function breakers are becoming the go-to. They cost more - typically $40-50 each versus $10-15 for a standard breaker - but you’re not stacking a GFCI outlet on top of an AFCI breaker, which can cause interaction issues anyway.
The code location chart: GFCI = wet/damp locations, AFCI = sleeping areas and most dwelling unit circuits (per 210.12), DFCI = where both apply simultaneously. When in doubt, install DFCI - you’ll never be wrong, and the price difference is minor compared to a callback.