- (US, usually, plural only, uncountable, countable) The alphabet. [First attested from around (1150 to 1350).]
- Do you know your ABC? (U.S.: Do you know your ABCs?)
- (obsolete, poetry) A type of poem in which the lines start with the letters of the alphabet in order. [Attested from around (1350 to 1470) until the mid 17th century.]
- (obsolete) A primer for teaching the Latin alphabet and first elements of reading. [Attested from around (1350 to 1470) until the mid 17th century.]
- The fundamentals of any subject. [First attested in the mid 16th century.]
- the ABC of finance
- (poker) A straightforward, uniform playing style, often focusing on betting for value, folding weak hands, and avoiding bluffing.
- (UK, rail transport) A British alphabetized guidebook for trains and their stations.
- German: Abc-Buch, ABC-Buch, Abecebuch, Abecedarium, Abcdarium, Buchstabierbuch, Lese-Lern-Buch, Lern-Lese-Buch, ABC-Fibel, Fibel
- Russian: а́збука
- (mnemonic, emergency medicine) Initialism of airway, breathing and circulation the essential steps in the immediate assessment and treatment of critically ill or injured patients.
- (US) Initialism of alcoholic beverage control
- Initialism of American-born Chinese
- Initialism of Australian-born Chinese
- (business management) Initialism of activity-based costing
- (climbing) Initialism of advance base camp
- (biochemistry) Initialism of ATP-binding cassette
- (immunology, medicine) Initialism of antigen-binding capacity
- (disease) Initialism of aneurysmal bone cyst
- (disease) Initialism of adenoid basal carcinoma
- (pharmaceutical drug) Abbreviation of abacavir#English|abacavir.
- (law, finance) Initialism of assignment for the benefit of creditors
- (electrical engineering) Initialism of absorbing boundary condition
- (programming) Initialism of abstract base class
- (psychology) Initialism of adventure-based counseling
- (television) Initialism of American Broadcasting Company an American commercial broadcast television network founded in 1943.
- (radio, television) Initialism of Australian Broadcasting Corporation [From 1983.]
- (historical, radio) Initialism of Australian Broadcasting Company [Founded in 1924.]
- (historical, radio, television) Initialism of Australian Broadcasting Commission [Founded in 1932.]
- (radio, television) Initialism of Asahi Broadcasting Corporation
- (finance) Initialism of Agricultural Bank of China
- (publishing) Initialism of Audit Bureau of Circulations
- (UK, historical) Initialism of Aerated Bread Company also A.B.C.
- (aviation) Initialism of Advance Booking Charter
- (historical, basketball) Initialism of Asian Basketball Confederation
- (historical, bowling) Initialism of American Bowling Congress
- Initialism of Santo André, São Bernardo do Campo and São Caetano do Sul satellite cities around the city of São Paulo that form the most important industrial area in Brazil.
- (US, rail) Initialism of Atlanta, Birmingham and Coast Railroad
- Initialism of an English-language bookstore in Amsterdam founded in 1972.
ABC (not comparable)
- (weaponry) Initialism of atomic, biological and chemical the three main categories of weapons of mass destruction.
- (slang, of a piece of chewing gum) Initialism of already been chewed
- (medicine, of diffuse large B-cell lymphoma) Initialism of activated B-cell-like