Quality of service (QoS) refers to the ability of a network or system to provide reliable and predictable performance under various conditions. This can include factors such as availability, reliability, latency, and throughput. QoS is important in ensuring that users receive a consistent and satisfactory level of service when using a network or system, particularly for applications that require real-time communication or depend on consistent performance, such as video streaming, VoIP, or online gaming. Researchers in this area focus on developing techniques and protocols to improve QoS, manage network resources effectively, and optimize performance for different applications and usage scenarios.