Packets per second (PPS) is a metric, one of the core rate units a thorough DDoS test is built to measure. It counts how many individual packets a target, router, firewall, or load balancer must process each second, independent of how large those packets are. PPS is the dimension that matters for protocol and packet-rate attacks: a flood of tiny 64-byte SYN or ACK packets can be modest in bits per second yet overwhelm a device's per-packet processing budget, interrupt handling, and stateful tables.
Why it matters in DDoS testing
Bandwidth and packet rate are different ceilings, and many devices fail on the second one first. A firewall rated for 10 Gbps of throughput may collapse far below that line when the traffic is small packets at high PPS, because each packet costs a table lookup. A test drives packet rate as an explicit axis to find where the per-packet ceiling sits.
The attack classes that push this metric are covered in understanding DDoS attack vectors.