In acoustics, volume compensation is a technique used to adjust the playback level of sound recordings so that they better match the original source material. The goal is to make the recording sound louder or softer, depending on the listener's preference.
There are two main types of volume compensation: compression and limiting. Compression reduces the dynamic range of a recording, making the loudest parts quieter and the quietest parts louder. Limiting does the same thing, but with a more drastic effect.
Both compression and limiting are often used together in order to achieve a desired result. For example, if you want a recording to be as loud as possible without distorting, you would first use compression to reduce its dynamic range, then use limiting to prevent clipping (a type of distortion caused by too much signal).
Volume compensation can be applied to any type of audio recording, but it's most commonly used with music recordings. It's also common in movies and television shows; many films and TV programs are compressed and limited so that they'll sound louder when played back on your TV or home theater system.
If you're not happy with the way a particular recording sounds, you can try adjusting its volume compensation settings. This can be done with most audio editing software; simply look for the compression or limiting options in your software's effects menu.