This is the burst size — the amount of traffic, in bytes, this egress QoS policy allows to exceed the steady-state rate limit before UCS starts dropping or remarking frames. This is the child object that actually carries the rate limit, burst size, and priority that get applied to outbound traffic on any vNIC or vHBA using the parent QoS policy. A burst value of 10240000 (roughly 10 MB) would let a vNIC using this policy briefly spike well above its steady rate — enough to absorb a short traffic burst — before enforcement kicks in.