I ran a search and found this on the STSC - Air Force site:
test factor is a system condition or parameter that has several options that need to be tested. Testing each option of each test factor once will find all single-mode faults which are faults not depending on any other parameters to occur. Some test factors interact incorrectly with one or more other test factor options causing multi-mode faults. The objective in combinatorial testing is to identify a minimum set of tests that will find all serious multi-mode faults. Often, all 2-way (pairs) and 3-way parameter combinations will find most multi-mode software faults.
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And according to Dictionary.com:
methˇodˇolˇoˇgy ( P ) Pronunciation Key (mth-dl-j)
n. pl. methˇodˇolˇoˇgies
1.) A body of practices, procedures, and rules used by those who work in a discipline or engage in an inquiry; a set of working methods: the methodology of genetic studies
2.) The study or theoretical analysis of such working methods.