True Peak Limiting is a method by which a limiter adjusts for how the digital waveform will be reconstructed by playback systems which can result in actual peak levels above 0dB even when the digital peak level is technically shown at below 0dB.
Implied Curvature
Basically the way intersample peaks occur is that the quantization points of a digital waveform can at times imply a curve between them which goes up a little bit higher than those actual sample points, resulting in a louder-than-expected actual peak level coming though.
To imagine it, just draw two dots in your mind, and then instead of drawing a straight line between them, draw a slightly curved line. The two dots are at a height of zero, and the curved line connecting them is bumping a little bit above zero. See?
