A person, who delights in having an intimate understanding of the internal workings of a system, computers and computer networks in particular. It is used to refer to someone skilled in the use of computer systems, especially if that skill was obtained in an exploratory way. The term is often misused in a pejorative context, where “cracker” would be the correct term. And due to that the term evolved to be applied to individuals, with or without skill, who break into security systems.
Several subgroups of the computer underground with different attitudes and aims use different terms to demarcate themselves from each other, or try to exclude some specific group with which they do not agree. In hackers culture there are many different categories, such as white hat (“ethical hacking”), grey hat, black hat and script kiddie. Usually the term cracker refers to black hat hackers, or more generally hackers with unlawful intentions.