Exploratory testing is one of the approach to test the software. With the rapid development and in Agile software development, Exploratory testing plays very important role.
In Exploratory Testing, Tester start testing the software without much knowledge of it also tester does not use any test cases to test the software. as name itself suggests Explore. Test start learn the software as well as start testing it. during testing Tester does not think in the box of software specifications or defined test plan and test cases. it helps to discover the issues which team does not thought of. best benefit of the exploratory testing to find usability and workflow related issues.
Exploratory testing mainly used when requirements and specifications are enough to create the test cases around it other types of testing you can found here : Link.