Crack

Crack or cracking means "to break or snap apart".

Chemical reaction

Cracking (chemistry), the decomposition of complex organic molecules into smaller ones.
Crack cocaine, a crudely freebased form of cocaine.

Computing

Cryptanalysis. "Cracking codes" can be a slang term for codebreaking.
Password cracking, the process of discovering the plaintext of an encrypted computer password.
System cracking, the defeating of security devices in computer networks, the process of gaining unauthorized access to a computer system (typically carried out by a black-hat hacker). Cracking can be defined as the act of entering a computer or computer network by force, whereas hacking does so by manipulation.
Software cracking, the defeating of software copy protection.

Economics

The value difference between a crude oil & oil products (usually per barrel) or different oil products, for instance a mogas crack - the difference between mogas & crude oil.

Anatomy and physiology

Gluteal cleft. Crack is sometimes a vulgarism for this separation between the buttocks.
Cracking knuckles
Vocal crack, a sharp change in vocal characteristics.

Homonyms and acronyms

Crack is a UNIX/Linux password cracking program for systems administrators.
Crack (also craic) is a dialect word common to Scotland and Ireland meaning "fun".
CRACK, an acronym for Children Requiring A Caring Kommunity. This program, based in Baltimore, Maryland, USA, pays drug users money to be sterilized and is now named Project Prevention.

See also