Definitions for "Hook flash"
Keywords:  cradle, pbx, hang, ath, centrex
Quickly depressing and releasing the plunger in or the actual handset-cradle to create a signal to a PBX or Centrex that special instructions will follow such as transferring the call to another extension.
The act of hanging up the telephone for a short period of time (one-half second). This operation is useful in PBX systems that interpret a hook flash as a signal to perform other services, such as transferring a call.
The dial modifier "!" causes the modem to go on-hook (hang-up) for one-half second. Also controlled by the ATH command.