Ad hoc testing
Ad hoc testing is a commonly used term for software testing performed without planning and documentation (but can be applied to early scientific experimental studies).
The tests are intended to be run only once, unless a defect is discovered. Ad hoc testing is the least formal test method. As such, it has been criticized because it is not structured and hence defects found using this method may be harder to reproduce (since there are no written test cases). However, the strength of ad hoc testing is that important defects can be found quickly.
It is performed by improvisation: the tester seeks to find bugs by any means that seem appropriate. Ad hoc testing can be seen as a light version of error guessing, which itself is a light version of exploratory testing.