(1) (Metal Oxide Semiconductor) See MOSFET.

(2) (Mean Opinion Score) The quality of a digitized voice line. It is a subjective measurement that is derived entirely by people listening to the calls and scoring the results from 1 to 5. Toll quality audio is generally considered to have a MOS rating of 4 and above.

The MOS is an average of the numbers for a particular codec. Because MOS testing requires carefully prepared and controlled test conditions, the best way to get a MOS test done is to have it outsourced. See codec.

An Objective Model
The E-Model is another rating system that provides an objective measurement of quality based on packet loss, jitter and delay. The E-Model reports results as R-values. Following is an approximate relationship between MOS and E-Model quality ratings.

 Subjective Interpretation         MOS    R-Value

 Excellent - almost all satisfied  4.5    90
 Very good - most users satisfied  4.0    80
 Good - some users dissatisfied    3.6    70
 Fair - many users dissatisfied    3.1    60
 Poor - most users dissatisfied    2.6    50
 Bad - not recommended             1.0     0