Black box Testing

Black box testing is functional testing, not based on any knowledge of internal software design or code. Black box testing is based on requirements and functionality. And is being tested to derive test cases from the specification.
The system is a black-box whose behavior can only be determined by studying its inputs and the related outputs
Black Box Testing is testing without knowledge of the internal workings of the item being tested. For example, when black box testing is applied to software engineering, the tester would only know the "legal" inputs and what the expected outputs should be, but not how the program actually arrives at those outputs. It is because of this that black box testing can be considered testing with respect to the specifications, no other knowledge of the program (code) is necessary.

Advantages of Black Box Testing
more effective on larger units of code than glass box testing
tester needs no knowledge of implementation, including specific programming languages
tester and programmer are independent of each other
tests are done from a user's point of view
will help to expose any ambiguities or inconsistencies in the specifications
test cases can be designed as soon as the specifications are complete
Disadvantages of Black Box Testing
only a small number of possible inputs can actually be tested, to test every possible input stream would take nearly forever
without clear and concise specifications, test cases are hard to design
there may be unnecessary repetition of test inputs if the tester is not informed of test cases the programmer has already tried
may leave many program paths untested
cannot be directed toward specific segments of code which may be very complex (and therefore more error prone)
most testing related research has been directed toward glass box testing.