This Recommendation provides a terminology which shall be used in conjunction with audio, video and audio-visual quality expressions in terms of Mean Opinion Score (MOS). This terminology is motivated by the intention to avoid misunderstanding as to whether specific values of MOS for audio are related to listening quality, talking quality or conversational quality, whether they originate from subjective tests, from objective models or from network planning models, as well as extending the concept to video and audio-visual quality. Furthermore, this Recommendation provides identifiers regarding the audio bandwidth, the type of interface (electrical or acoustical), and the video resolution. Further guidance on the interpretation of MOS is given in Rec. P.800.2.