This post gives and explains definition of Black Box Software Testing approach that is given by Black Box Software Testing Foundations course (BBST) created by Rebecca Fiedler, Cem Kaner and James Bach.
As a software tester in Agile team, in order to earn recognition by other team members, you need to be able to explain how you do software testing. Black Box Software testing approach is most used approach.
Here is Black Box Software Testing approach definition given by BBST:
Testing and test design without knowledge of the code.
The code is source code of the product that you test.
Testing is activity, based on your test design, you are performing the investigation of product under test.
You may not know anything about the code (e.g. you can not read source code because you do not understand it), or you may not use on purpose that knowledge (you can read the source code, but you do not want to bias your test design based on that knowledge).
It is important to state that testing against authoritative specification (requirements) is only a small portion of black box approach. Black box software tester is expert in product interaction with world in which runs, where world is:
hardware and software environment
users of product
domain that is automated (domain example is Google search engine, that automates your quest in searching web pages with specific information).
Black box software tester designs tests (experiments) based on conducted research on the product environment. E.g. for Google search engine, you would first conduct research how Google automatically categorizes web pages.