Booters are also known as booter services, are on-demand DDoS (Distributed-Denial-of-Service) attack services offered by enterprising criminals in order to bring down websites and networks. In other words, booters are the illegitimate use of IP stressers.
An IP stresser is a tool which is designed to test a network or server for robustness. The administrator may run a stress test in order to determine whether an existing resources (bandwidth, CPU, etc.) are sufficient to handle additional load.