3letter

3letter is an informal label used to refer to any sequence of three consecutive letters from the Latin alphabet. The term is commonly encountered in discussions of abbreviations, codes, and letter-pattern analysis, and it is often used as shorthand for three-letter abbreviations or three-letter codes.

In linguistics and natural language processing, three-letter sequences are studied as trigrams. Trigrams are used to build statistical language models, support spelling correction and text prediction, and assist in pattern recognition and search tasks. They help researchers understand orthographic and phonotactic tendencies in languages and can be applied to tasks such as text classification and anomaly detection.

In computing and standardization, three-letter codes are widely used. Historical computing environments imposed short extensions, with three-character file extensions shaping early software practices. Today, three-letter identifiers remain common in several domains: IATA airport codes (three-letter codes for airports), ISO 4217 currency codes (three-letter codes for currencies), and ISO 639 language codes (which include short three-letter variants in some contexts). The three-letter form remains a compact and widely interoperable convention for concise designation.

Usage notes indicate that 3letter is not a formal technical term with a single official definition. Instead, it functions as a descriptive shorthand for strings, codes, or patterns consisting of exactly three letters. In formal writing, it is usually clearer to refer directly to three-letter sequences, three-letter abbreviations, or specific code standards.

See also: Trigram, three-letter acronym, IATA airport codes, ISO 4217 currency codes, ISO 639 language codes.