High Speed Sync (HSS)
Technique
A flash mode that allows the flash to be used at shutter speeds above the normal sync limit.
Normally flash sync is limited to 1/200-1/250 sec. With HSS the flash can be used at 1/1000 sec or higher, crucial for outdoor portraits in bright sun to keep the aperture wide (f/1.8) without overexposing the background. HSS costs flash power: range drops significantly.
Tools that help with this: