A peak-hold indicator freezes the maximum: the meter bar dances with the signal while a thin cap sits at the loudest recent moment, decaying slowly or holding until reset. Engineers rely on it because peaks matter (clipping lives there) and eyes miss single-frame events.
The behavior is also quietly great motion design. The two time scales in one element, instant attack and slow decay, give meters their satisfying physicality, and generations of players copied the pattern for good reason.
Photism’s signal scene meters implement true peak hold because the scene’s promise is studio-grade instrumentation rendered in the palette, and peak behavior is where fake meters give themselves away.