True peak is the real maximum level of the analog waveform a DAC will reconstruct, which can sit higher than the loudest digital sample. Between samples the smooth reconstructed signal can overshoot — inter-sample peaks — so a track that never exceeds 0 dBFS in the sample domain can still drive a converter or a lossy encoder into distortion. True-peak meters estimate this by oversampling before measuring, and the result is reported in dBTP. This is why loudness standards set true-peak ceilings (-1 dBTP for EBU R128, often -2 dBTP for lossy delivery): the margin absorbs inter-sample peaks and the extra overshoot that encoding to AAC or Opus can introduce.
