Recommendation ITU‑T E.800 provides a set of commonly used terms in the study and management of quality of service (QoS). The technical and non-technical terms related to the QoS listed in this Recommendation are intended to represent the interests of all parties of telecommunications service market, i.e., user, service provider, manufacturer and regulator.

The definition of terms is in the context of QoS. Some terms may be defined differently in other documents in another context. Therefore, care should be taken in the use of such terms in their appropriate context. For a comprehensive set of QoS terms, one is referred to Recommendations related to specific services or performance characteristics.