that test cases are designed in advance, including steps to reproduce and expected results. These tests are later performed by a tester who compares the actual result with the expected.
When performing exploratory testing, there are no exact expected results; it is the tester that decides what will be verified, critically investigating the correctness of the result.
In reality, testing almost always is a combination of exploratory and scripted testing, but with a tendency towards either one, depending on context.
The documentation of exploratory testing ranges from documenting all tests performed to just documenting the bugs. During pair testing, two persons create test cases together; one performs them, and the other documents.
Advantages & Disadvantages:
The main advantage of exploratory testing is that less preparation is needed, important bugs are found fast, and is more intellectually stimulating than scripted testing.
Another major benefit is that testers can use deductive reasoning based on the results of previous results to guide their future testing on the fly. They do not have to complete a current series of scripted tests before focusing in on or moving on to exploring a more target rich environment. This also accelerates bug detection when used intelligently.
Another benefit is that, after initial testing, most bugs are discovered by some sort of exploratory testing. This can be demonstrated logically by stating, "Programs that pass certain tests tend to continue to pass the same tests and are more likely to fail other tests or scenarios that are yet to be explored."
Disadvantages are that the tests can't be reviewed in advance (and by that prevent errors in code and test cases), and that it can be difficult to show exactly which tests have been run.
When repeating freestyle exploratory tests, they will not be performed in the exact same manner, which can be an advantage if it is important to find new errors; or a disadvantage if it is more important to know that exact things are functional.
Exploratory testing is extra suitable if requirements and specifications are incomplete, or if there is lack of time. The approach can also be used to verify that previous testing has found the most important defects.