Crack or cracking means "to break or snap apart". It also may mean:

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.
• Security 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

• Craic, a word used in 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.