Active testing, a testing technique, where the user introduces test data and analyses the result.
During Active testing, a tester builds a mental model of the software under test which continues to grow and refine as your interaction with the software continues.
At the end of each and every action performed on the application under test, we need to check if the model/application seems to fulfill client's needs.
If not, the application needs to be adapted, or that we got a problem in the application. We continuously engage in the testing process and help us to come up with new ideas, test cases, test data to fulfill.
At the same time, we need to note down things, which we might want to turn to later or we follow up with the concerned team on them, eventually finding and pinpointing problems in the software.
Hence, any application under test needs active testing which involves testers who spot the defects.