A performance baseline records metrics such as response time, throughput, resource use or page-rendering speed under defined conditions. It establishes the starting point before optimization work begins.
Consistent test conditions make changes comparable. Without a baseline, a faster or slower result may come from different data, hardware, network conditions or test steps rather than the implementation change.
ELI5
A performance baseline is the starting stopwatch result. You measure how fast the system is now so you can tell whether a later change truly helped.
For example, a team may load the same page with the same test data five times before and after a fix, then compare the typical loading time.
