Hacking, as a general term, is used to refer to the creative process of breaking or enhancing systems and processes. In this context, system hacking can be applied to the human biome, in which case a hack would mean something like increasing recovery time or seeing in the dark; likewise, a system can be the way a building is constructed, in which case a hack could mean putting up scaffolding 3x as fast for 2x less cost.
When in dealing with technology, more specifically software, hacking is the dark art of circumventing the encryption & security of an application in pursuit of private or proprietary data. A pronounced example is the hacking that effects nation-states, where military intelligence can be stolen and then used against the nation from which it was stolen.