The recycle time is the time taken by a flash to build up the power for the next flash after it’s just been used. Flashguns work by accumulating a large electrical charge which is then discharged in an instant via the flash head.
The time taken to re-accumulate this charge – the recycle time – varies from one flash to another, and it’s a key selling point. Busy professional photographers will want the recycle time to be as short as possible.
Regular flashguns of the type built into cameras or clipped on to the the accessory shoe may have a recycle time of several seconds. Professional studio flash systems may recycle in a second or less.
The recycle time is shorter if the flash is not used at full power. Many shots will be taken at reduced power because the subject is close or because the flash is being balanced with the available light or other flash units.