The term CENTER X can be solved by two three-letter words, HUB and TAC. HUB is an abbreviation for 'HUB of activity' and is used to refer to a place or person that is the focus of attention or activity. TAC is an abbreviation for 'tactical center' and is used to refer to a place where military operations are planned and coordinated. Together, these two words form the term CENTER X, which is used to describe a place or person that is the focus of both activity and military operations.