Black box testing is a software testing method where the internal structure, design, and implementation of the system are not known to the tester. The tester focuses on testing the functionality of the software without looking at the code. This type of testing is based on requirements and specifications, and it helps in finding errors or bugs in the software.

During black box testing, the tester interacts with the software as an end-user and tests the input and output without any knowledge of the internal logic of the system. This method is useful for validating the correctness and completeness of the software application.