Resampling is the process of recalculating samples in a sound file at a different rate than the file was originally recorded.

If a sample is resampled at a lower rate, sample points are removed from the sound file decreasing its size, but also decreasing its available frequency range.

When resampling to a higher sample rate, extra sample points in the sound file are interpolated. This increases the size of the sound file but does not increase the quality.

When down-sampling, you need to be aware of a type of distortion called "aliasing."