Transient
noun
Something which is transient.
A transient phenomenon, especially an electric current; a very brief surge.
(acoustics) A relatively loud, non-repeating signal in an audio waveform which occurs very quickly, such as the attack of a snare drum.
adjective
Passing or disappearing with time; transitory.
“a transient pleasure”
Remaining for only a brief time.
“a transient disease”
Decaying with time, especially exponentially.
Synonyms: brief, ephemeral, fleeting, flighty, fugacious, passing, temporary, transitory