Testing an application performance with respect to 
different user loads is called performance testing

Performance Testing is the process of cecking the behaviour 
of the application with the new environment/new 
settings/Configuration.

Not all software systems have specifications on performance 
explicitly. But every system will have implicit performance 
requirements. The software should not take infinite time or 
infinite resource to execute. "Performance bugs" sometimes 
are used to refer to those design problems in software that 
cause the system performance to degrade. 

Performance has always been a great concern and a driving 
force of computer evolution. Performance evaluation of a 
software system usually includes: resource usage, 
throughput, stimulus-response time and queue lengths 
detailing the average or maximum number of tasks waiting to 
be serviced by selected resources. Typical resources that 
need to be considered include network bandwidth 
requirements, CPU cycles, disk space, disk access 
operations, and memory usage The goal of performance 
testing can be performance bottleneck identification, 
performance comparison and evaluation, etc. The typical 
method of doing performance testing is using a benchmark -- 
a program, workload or trace designed to be representative 
of the typical system usage.