Instrumentation is an ability to monitor or measure the level of a product's performance, to diagnose errors, and to write trace information. Programmers implement instrumentation in the form of code instructions that monitor specific components in a system (for example, instructions may output logging information to appear on screen). When an Application contains instrumentation code, it can be managed using a management tool. Instrumentation is necessary to review the performance of the application. Instrumentation approaches can be of two types:
Source: https://stackoverflow.com/questions/8755211/what-is-meant-by-the-term-instrumentation