Flash Sync Speed and Exposure Time
The flash sync speed (short for „synchronization speed“) is the shortest exposure time that your camera can use with a flash.
It is depending on the mechanics of the shutter that opens and closes an opening to let light fall onto the image sensor.
During the short time of the flash burst the shutter must be completely open across the whole are of the image sensor and this is not the case when exposure times get too short.
In other words: The exposure time is longer than the flash duration.
Typical flash sync speeds are between 1/250 s und 1/125 s at DSLR cameras, sometimes only 1/60 s.
For compact cameras the manufacturers usually do not mention explicitly flash sync speeds but they can have shorter (better) sync speeds.
The flash sync speed does not matter if you use the flash in low light. But it can be a limitation when you use fill flash in bright daylight – then the camera needs possibly to close the aperture to avoid overexposure because the exposure time cannot be reduced further. This decreases the range of your flash.
Some (more expensive) cameras offer tricks to use the flash at any exposure time, even the very shortest ones but these are kept for a separate article with more advanced features.
The longest exposure time that you can use with a flash has no technical limitation like the shortest one. But for practical reasons cameras do not exceed a certain exposure time to avoid risk of blurred pictures. This longest exposure time is typically 1/60 s and depending on the settings that your camera offers it may be possible to adjust it.
But you can instruct the camera to ignore this limitation and to expose as long as needed, see the option for slow flash synchronization in the next chapter.