Quality of Service - network management technique for prioritizing certain types of traffic. Like having express lanes for emergency vehicles while regular traffic uses standard lanes.
Video conferencing applications use QoS to ensure voice and video data gets priority over file downloads.
QoS (Quality of Service) is a networking capability rather than a single cloud product. All major clouds support QoS-like traffic prioritization using a combination of network policies (e.g., DSCP marking), routing, and bandwidth/priority controls on VPNs, interconnects, load balancers, and SD-WAN/virtual appliances. Exact features and where QoS is enforced depend on the service (VPN, dedicated interconnect, virtual router/firewall) and the on-premises network.