Downsampling (or subsampling) is the process of reducing the sampling rate of a signal. This is usually done to reduce the data rate or the size of the data. For details, please refer to this wikipedia link.

A paper by Mitchel Weintraub and Leonardo Neumeyer called CONSTRUCTING TELEPHONE ACOUSTIC MODELS FROM A HIGH-QUALITY SPEECH CORPUS provides some background on the use of downsampled High Quality Speech Audio in applications that can only use lower sampling rates.