1: "A style of software testing that emphasizes the personal freedom and responsibility of the individual tester to continually optimize the quality of his/her work by treating test-related learning, test design, test execution, and test result interpretation as mutually supportive activities that run in parallel throughout the project." - C. Kaner

2: "Exploratory testing is simultaneous learning, test design, and test execution.” - J. Bach

3: "Simultaneously designing and executing tests to learn about the system, using your insights from the last experiment to inform the next." - E. Hendrickson