dBTP
When a digital file is played back, the content of the file will be converted from digital to analog to be able to hear it through a speaker. The data at hand is organized in samples that carry the amplitude taken at frequent steps in time.
The gaps inbetween those steps are calculated through a reconstruction filter during the conversion progress to produce a flawless and smooth sound wave. The calculated amplitudes (also called intersample peaks) may happen to be louder than the highest level stored in the digital file.
These louder amplitudes define the true peak of the file. dBTP expresses the distance from 0 dB (maximum amplitude of digital file) to the true peak in dB (decibel). It is an important measure, with which the mastering engineer can avoid clipping or distortion that may happen on playback systems, simply by adding enough headroom into the master files.