A booter (or stresser) is commercialized DDoS attack infrastructure, a rented service that sells attack traffic on demand, and the floods it produces are what a controlled, authorized DDoS test safely and lawfully reproduces. Marketed euphemistically as "stress-testing" tools, booters give a paying customer a web dashboard to point pre-built botnets and reflection infrastructure at a target, lowering the skill and cost of launching an attack to almost nothing.
Why it matters in DDoS testing
Booters define the realistic low end of the threat. A service can be hit not only by sophisticated adversaries but by a disgruntled user with a small subscription, which means even modest targets need a validated floor of resilience. The traffic is real, multi-vector, and globally sourced. The only difference between a booter and a legitimate test is authorization and scope: one is criminal, the other is a contracted, bounded exercise.
For what a measured resilience baseline looks like, see DDoS Resilience Testing.