Flash duration is the amount of time the light produced from a strobe is available. A faster duration will allow you to catch things like water droplets or glass breaking, things not possible with slower durations.
The fastest flash duration from a speedlight is when it's on it's lowest power setting. Generally 1/128th power.
The complete opposite is true for a studio strobe. Their flash flash duration is typically at full power. Confusing right.
That's something to keep in mind if you want to freeze as much action as possible.