Hacker is a term that is used to mean a variety of different things in computing. Depending on the context, the term can refer to a person in any one of several distinct (but not completely disjoint) communities and hacker subcultures:
Hacker (computer security). People involved with circumvention of computer security. This primarily concerns unauthorized remote computer break-ins via communication networks such as the Internet (Black hats), but also includes those who debug or fix security problems (White hats), and the morally ambiguous Grey hats.