Combinatorial testing seeks to test the interactions between different parameters that affect the system. "Pairwise" aka "all-pairs" is a combinatorial testing technique.

Combinatorial testing seeks to test the interactions between different parameters that affect the system. "Pairwise" aka "all-pairs" is a combinatorial testing technique, based on the idea that most faults result from the interaction of two factors, so test suites based on combinations of pairs will still be effective at finding issues.

Further reading:

This site has a great list of resources: http://www.combinatorialtesting.com/clear-introductions-1