we cannot categorize that under Unplanned Adhoc testing. This world has got its electric light because of the exploration of Thomas Alwa Edison. This world has got its Air Traffic because of the exploration of Right Brothers. Exploration is the one which is going to fetch good results and remarkable results at the end. Exploration at the time of designing the tests is very much needed for a complex application to plan for the areas which is new for the tester and the areas which are old to him need not to be planned for test as he is good enough with finding bugs with Exploratory Testing for those areas. Even if the tests for that complex parts of the application are not planned also, they can be done at the time of execution if the tester is having expertise in testing and that too in Exploratory Testing, very much.
Designing the tests is also an art and it also involves creativity in itself. It is the different ways of thinking of the tester as an individual which is put into papers and termed as Test Plan. Testing is a mindset. The interpretation of the information differs from people to people. If this is the case then coverage of testing can be achieved by more than one people testing the same piece of code. Thus with the different ways of exploration, we can achieve the coverage.
If the exploration is done on Test Application for testing that, then that is termed as Exploratory Testing. If the exploration is done on Test Application for designing the tests then that is termed as Test Planning. Whatever the terms used, Exploration in testing is very much in need.