To quiesce is to pause or alter a device or application to achieve a consistent state, usually in preparation for a backup or other maintenance.
In software applications that modify information stored on disk, this generally involves flushing any outstanding writes; see buffering.
With telecom applications, this generally involves allowing existing callers to finish their call but preventing new calls from initiating.
For an application to be quiesced during the shadow copy process, it must register itself as a writer[2] and it is responsible for putting itself into a quiescent mode upon notification.
Various database and application vendors implement schemes to provide support for this feature including: The dictionary definition of quiesce at Wiktionary