Peak level is the instantaneous maximum amplitude of a signal — the single highest sample in the sample domain. Peak meters are essential for one job: making sure you never exceed 0 dBFS and clip. But peaks say almost nothing about how loud something sounds. A sharp transient like a snare hit can peak high while contributing little to perceived loudness, and two clips that peak identically can differ widely in loudness. That gap is why peak metering, useful as a safety check, was replaced by RMS and ultimately LUFS for any judgement about loudness, leaving peak (and true peak) to guard the ceiling.
