Loudness is the keyword to describe a new method for measuring audio levels in files.
We used to evaluate levels by looking at the peaks but you will see that there is a much better way now.
This new measuring method is much more representative of what the human ear perceives.
It allows for consistent levels within and between programs!
I recommend the following standard for speech-based content:
Programm Loudness for stereo (Lk): -16 LUFS ±1 LU
Programm Loudness for mono (Lk): -19 LUFS ±1 LU
Max Loudness Range (LRA): 8 LU
Max True Peaks (TP): -1 dBTP
Go to the sub-pages for more details on the technical background and application of Loudness.