Performance testing involves testing a system to determine how it performs under a particular workload. The document discusses various types of performance testing like load/capacity testing, stress testing, volume testing, endurance testing, and spike testing. It also discusses concepts like bottlenecks, prerequisites for performance testing, popular load testing tools like JMeter, and how to use key JMeter features for performance testing like adding users, HTTP requests, listeners, parameterization, correlation, assertions, and distributed testing.