Martin Fowler

Exploratory testing is a style of testing that emphasizes a rapid cycle of learning, test design, and test execution. Rather than trying to verify that the software conforms to a pre-written test script, exploratory testing explores the characteristics of the software, raising discoveries that will then be classified as reasonable behavior or failures.

The exploratory testing mindset is a contrast to that of scripted testing. In scripted testing, test designers create a script of tests, where each manipulation of the software is written down, together with the expected behavior of the software. These scripts are executed separately, usually many times, and usually by different actors than those who wrote them. If any test demonstrates behavior that doesn’t match the expected behavior designed by the test, then we consider this a failure.

For a long time scripted tests were usually executed by testers, and you’d see lots of relatively junior folks

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