In the world of software testing, system testing is the testing of a complete and fully integrated software product.
Usually software is only one element of a larger computer based system. Ultimately, software is interfaced with other software/hardware systems. System testing is actually a series of different tests whose sole purpose is to exercise the full computer based system.
System testing falls under the black box testing category of software testing. White box testing is the testing of the internal workings or code of a software application. In contrast, black box or system testing is the opposite.System testing involves the external workings of the software from the user's perspective.