A jiffy is an informal flash of time. In a jiffy, back in a jiffy, wait a jiffy.
It always appears in a jiffy, meaning very soon, and it is friendly rather than precise. Physics has borrowed it as a real unit, and unhelpfully defines it differently in different fields — in one, roughly the time light takes to cross a centimetre.
1nounjiffyA very short moment of time.
“Wait there, I'll be back in a jiffy with your coffee.”
jiffy is a moment.
The origin is unknown; it was said to be thieves' slang for lightning in the eighteenth century.
Origin unknown; said to have been thieves’ cant for “lightning”. Also formerly written "giffy", to which a connection with gliff has been proposed. As a kind of envelope, a genericization of Jiffy bag.
Etymology from Wiktionary, CC BY-SA