What Is The Difference Between Performance, Load, Volume & Stress Testings?

Performance testing measures response times across various system layers, and identifies potential bottlenecks that may exist. Ideally, the system being tested is already functionally stable.
Load testing is often a part of the larger performance testing strategy.
It is different from performance testing, in that performance testing may measure response time with a single user exercising the system or with multiple users exercising the system. Load testing, however, focusing on increasing the load on the system to some stated or implied maximum load, to verified the system can handled defined system boundaries.
Volume testing is often considered synonymous with load testing, yet volume testing focuses on data.
Stress testing goes to the next level with respect to the quantity of users or data place in the system. The intent is to go beyond testing stated or implied boundaries, and identify actual boundaries by identifying the precise load at which the system breaks (its resources are overwhelmed to the point it ceases to function properly)